Facet joint replacement instruments and methods

ABSTRACT

A facet joint replacement system includes an inferior implant with an inferior articular surface, a superior implant with a superior articular surface, and an optional crossbar. The inferior implant and the superior implant are each polyaxially adjustably connected to fixation elements which anchor the implants to adjacent vertebrae. The optional crossbar may be polyaxially adjustably connected to bilateral implants. The system components may be provided in kits which provide components of various sizes and shapes. A set of surgical instruments may facilitate implantation of the facet joint replacement system by providing tools for bone preparation, trialing, implant insertion, implant alignment, and lock-out of modular interconnections.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 12/630,534, filed Dec. 3, 2009, now pending, whichis entitled FACET JOINT REPLACEMENT INSTRUMENTS AND METHODS, and whichis a continuation-in-part of:

U.S. patent application Ser. No. 12/240,320, filed Sep. 29, 2008,entitled SPINAL FACET JOINT IMPLANT, which is now issued as U.S. Pat.No. 8,906,063.

U.S. patent application Ser. No. 12/240,320 is a divisional of U.S.patent application Ser. No. 10/860,487, filed Jun. 2, 2004, entitledSPINAL FACET JOINT IMPLANT, which is now issued as U.S. Pat. No.8,926,700.

U.S. patent application Ser. No. 10/860,487 claims the benefit of:

U.S. Patent Application 60/545,101, filed Feb. 17, 2004, entitledSPHERICAL IMPLANT AND BONE BED; and

U.S. Patent Application 60/545,094, filed Feb. 17, 2004, entitledSPHERICAL ARTICULATING IMPLANT SURFACE.

U.S. patent application Ser. No. 12/630,534 is also acontinuation-in-part of:

U.S. patent application Ser. No. 12/201,046, filed Aug. 29, 2008,entitled SYSTEM AND METHOD FOR FACET JOINT REPLACEMENT, which is nowissued as U.S. Pat. No. 8,308,768;

U.S. patent application Ser. No. 12/201,086, filed Aug. 29, 2008,entitled SYSTEM AND METHOD FOR IMPLANT ANCHORAGE WITH ANTI-ROTATIONFEATURES, which is pending;

U.S. patent application Ser. No. 12/201,128, filed Aug. 29, 2008,entitled SYSTEM AND METHOD FOR FACET JOINT REPLACEMENT, which is nowissued as U.S. Pat. No. 8,252,027;

U.S. patent application Ser. No. 12/201,148, filed Aug. 29, 2008,entitled SYSTEM AND METHOD FOR FACET JOINT REPLACEMENT WITH DETACHABLECOUPLER, which is now issued as U.S. Pat. No. 8,206,418; and

U.S. patent application Ser. No. 12/201,198, filed Aug. 29, 2008,entitled SYSTEM AND METHOD FOR FACET JOINT REPLACEMENT, which is nowissued as U.S. Pat. No. 8,211,147.

U.S. patent application Ser. Nos. 12/201,046; 12/201,086; 12/201,128;12/201,148; and 12/201,198 are each continuations-in-part of:

U.S. patent application Ser. No. 12/104,726, filed Apr. 17, 2008,entitled FACET JOINT REPLACEMENT, which is now issued as U.S. Pat. No.8,353,933; and

U.S. patent application Ser. No. 12/104,855, filed Apr. 17, 2008,entitled FACET JOINT REPLACEMENT, which is now issued as U.S. Pat. No.8,333,789.

U.S. patent application Ser. Nos. 12/201,086; 12/201,128; 12/201,148;12/104,726; and 12/104,855 each claim the benefit of:

U.S. Application No. 61/023,927, filed Jan. 28, 2008, entitled AFRSGENERATION II INSTRUMENTS;

U.S. Application No. 61/033,473, filed Mar. 4, 2008, entitled TOPLOADING RECEIVER FOR AN ADJUSTABLE FACET REPLACEMENT;

U.S. Application No. 61/040,041, filed Mar. 27, 2008, entitled FACETJOINT REPLACEMENT;

U.S. Application No. 61/042,896, filed Apr. 7, 2008, entitled SPINALFIXATION ON AN IMPLANT BASE; and

U.S. Application No. 61/045,526, filed Apr. 16, 2008, entitled INFERIORBASE-SPLIT CLAMP AND MULTI-LEVEL SPLIT CLAMP.

U.S. patent application Ser. Nos. 12/104,726 and 12/104,855 are alsocontinuations-in-part of U.S. patent application Ser. No. 11/972,158,filed Jan. 10, 2008, entitled TAPER-LOCKING FIXATION SYSTEM, which isnow issued as U.S. Pat. No. 8,900,273.

U.S. patent application Ser. No. 11/972,158 claims the benefit of:

U.S. Patent Application 60/884,233, filed Jan. 10, 2007, entitledTAPER-LOCKING ROD FIXATION SYSTEM;

U.S. Application No. 60/912,323, filed Apr. 17, 2007, entitled AFRSMULTI-LEVEL IMPLANT SYSTEM;

U.S. Application No. 60/968,324, filed Aug. 28, 2007, entitledINTERVERTEBRAL DISC IMPLANT WITH FACET MOTION CONSTRAINTS;

U.S. Application No. 60/950,012, filed Jul. 16, 2007, entitled INFERIORFACET IMPLANT HOLDER WITH CLAMP RETENTION;

U.S. Application No. 60/950,021, filed Jul. 16, 2007, entitled MONORAILINSTRUMENT GUIDANCE SYSTEM FOR LUMBAR SPINAL SURGERY;

U.S. Application No. 60/950,031, filed Jul. 16, 2007, entitled LINEARPOLYAXIAL LOCKING MECHANISM WITH TOOL;

U.S. Application No. 60/950,038, filed Jul. 16, 2007, entitled MOBILEINFERIOR FACET BEARING WITH SUPERIOR CLIP;

U.S. Application No. 60/957,505, filed Aug. 23, 2007, entitled DYNAMICSTABILIZATION AND STATIC FIXATION OPTIONS FOR FACET REPLACEMENTPROSTHESIS;

U.S. Application No. 60/968,925, filed Aug. 30, 2007, entitled SYSTEMSAND METHODS FOR LESS INVASIVE FACET JOINT REPLACEMENT;

U.S. Application No. 61/015,866, filed Dec. 21, 2007, entitledINTERVERTEBRAL DISC IMPLANT WITH FACET MOTION CONSTRAINTS INCLUDINGPOSTERIOR COMBINATION DISCS;

U.S. Application No. 61/015,876, filed Dec. 21, 2007, entitledINTERVERTEBRAL DISC IMPLANT WITH FACET MOTION CONSTRAINTS AND METHODSFOR IMPLANT ALIGNMENT;

U.S. Application No. 60/975,731, filed Sep. 27, 2007, entitledMONOLITHIC INFERIOR IMPLANT STRUT WITH INTEGRAL CROSS LINK CLAMP;

U.S. Application No. 60/984,798, filed Nov. 2, 2007, entitled LOWPROFILE POLYAXIAL FACET IMPLANT;

U.S. Application No. 60/984,814, filed Nov. 2, 2007, entitled HINGEDEYELET SCREW;

U.S. Application No. 60/984,983, filed Nov. 2, 2007, entitled ADJUSTABLEFACET IMPLANT BASE PIECE;

U.S. Application No. 60/984,434, filed Nov. 1, 2007, entitled SUPERIORINSTRUMENT;

U.S. Application No. 60/984,428, filed Nov. 1, 2007, entitled CROSS LINKCLAMP;

U.S. Application No. 60/984,594, filed Nov. 1, 2007, entitled ADJUSTABLEINFERIOR FACET REPLACEMENT WITH MEDIAL-LATER SLIDE ADJUSTMENT;

U.S. Application No. 61/014,344, filed Dec. 17, 2007, entitled INFERIORSTRUT UPDATE;

U.S. Application No. 61/015,886, filed Dec. 21, 2007, entitled EYELETPEDICLE SCREW WITH MULTI-AXIAL FIXATION; and

U.S. Application No. 61/015,840, filed Dec. 21, 2007, entitled CERVICALPLATE WITH FACET MOTION CONTROL.

U.S. patent application Ser. No. 11/972,158 is a continuation-in-part ofU.S. patent application Ser. No. 11/063,941, filed Feb. 22, 2005,entitled POLYAXIAL ORTHOPEDIC FASTENING APPARATUS, which is now issuedas U.S. Pat. No. 7,993,373; and

U.S. patent application Ser. No. 11/312,323, filed Dec. 19, 2005,entitled POLYAXIAL ORTHOPEDIC FASTENING APPARATUS WITH INDEPENDENTLOCKING MODES, which is now issued as U.S. Pat. No. 8,062,336.

U.S. patent application Ser. No. 11/312,323 is a continuation-in-part ofU.S. patent application Ser. No. 11/063,941, filed Feb. 22, 2005,entitled POLYAXIAL ORTHOPEDIC FASTENING APPARATUS, which is now issuedas U.S. Pat. No. 7,993,373.

All of the above-referenced documents are hereby incorporated byreference in their entirety.

BACKGROUND OF THE INVENTION The Field of the Invention

The invention relates to spinal surgery. More specifically, theinvention relates to replacement of natural vertebral facet joints withimplantable artificial facet joint replacements.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope.

FIG. 1 is a perspective view of a portion of a spine with a bi-lateralfacet joint replacement system implanted into two adjacent vertebrae;

FIG. 2 is perspective view of an inferior facet joint implant coupled toa crosslink rod;

FIG. 3 is an exploded view of the inferior facet joint implant andcrosslink rod of FIG. 2;

FIG. 4 is a partial cross-sectional view of an attachment mechanism ofthe facet joint implant of FIG. 2;

FIG. 5 is a perspective view of an inferior implant body coupled to aclip;

FIG. 6 is a perspective view of the clip of FIG. 5 and a plug;

FIG. 7A is a perspective view of an alternate embodiment of a clip; andFIG. 7B is a perspective view of the clip of 7A coupled to an alternateembodiment of an inferior facet joint implant;

FIG. 8A is a perspective view of an alternate embodiment of an inferiorfacet joint implant coupled to a crosslink rod; and FIG. 8B is anexploded view of the inferior facet joint implant and crosslink rod ofFIG. 8A;

FIG. 9A is a plan view of an inferior articular body of the inferiorfacet joint implant of FIG. 8; and FIG. 9B is a cross-sectional view ofthe inferior articular body of FIG. 9A;

FIG. 10A is a perspective view of an alternate embodiment of a clip;FIG. 10B is a front view of the clip of FIG. 10A; and FIG. 10C is across-sectional view of the clip of FIG. 10A;

FIG. 11 is a perspective view of a fixation assembly secured to aninferior strut;

FIG. 12 is an exploded view of the fixation assembly and inferior strutof FIG. 11;

FIG. 13A is a lateral view of a fixation assembly base member; FIG. 13Bis a posterior view of the fixation assembly base member of FIG. 13A;FIG. 13C is an anterior perspective view of the fixation assembly basemember of FIG. 13A; and FIG. 13D is a cross-sectional view of thefixation assembly base member of FIG. 13A;

FIG. 14A is a lateral perspective view of an alternate fixation assemblybase member; and FIG. 14B is a cross-sectional view of the fixationassembly base member of FIG. 14A;

FIG. 15 is a lateral perspective view of an alternate fixation assemblybase member;

FIG. 16 is a lateral perspective view of an alternate fixation assemblybase member;

FIG. 17 is a lateral perspective view of an alternate fixation assemblybase member; zoo

FIG. 18 is a lateral perspective view of an alternate fixation assemblybase member;

FIG. 19 is a lateral perspective view of an alternate fixation assemblybase member;

FIG. 20 is a lateral perspective view of an alternate fixation assemblybase member;

FIG. 21 is a perspective view of an alternate embodiment of a fixationmember;

FIG. 22 is a perspective view of a fixation assembly secured to asuperior facet joint implant;

FIG. 23 is a perspective view of an alternate fixation assembly securedto an alternate embodiment of a superior facet joint implant;

FIG. 24 is an exploded view of the alternate fixation assembly andsuperior facet joint implant of FIG. 23;

FIG. 25 is a cross-sectional view of the alternate fixation assembly andsuperior facet joint implant of FIG. 23;

FIG. 26 is a perspective view of the clip of FIG. 5 coupled to aninferior facet joint implant, and the superior facet joint implant andfixation assembly of FIG. 23;

FIG. 27 is a perspective view of the inferior and superior facet jointimplants of FIG. 26 joined by the clip of FIG. 5;

FIG. 28 is a perspective view of the clip and inferior implant of FIG. 7coupled to a delivery tool, and the superior facet joint implant andfixation assembly of FIG. 23;

FIG. 29 is a perspective view of the clip and inferior implant of FIG. 7coupled to a flexing tool, coupled to the superior facet joint implantand fixation assembly of FIG. 23;

FIG. 30A is a perspective view of the clip of FIG. 10 coupled to theinferior implant of FIG. 8, the superior implant of FIG. 23, and aninserter tool; FIG. 30B is a side view of the clip, inferior implant,superior implant, and inserter tool of FIG. 30A;

FIG. 31 is a perspective view of a screw driver;

FIG. 32 is a detail view of a collet and a distal tip component of thescrew driver of FIG. 31;

FIG. 33 is a detail view of the distal tip of FIG. 32;

FIG. 34A is a side view of the screw driver of FIG. 31 in an unlockedconfiguration;

FIG. 34B is a cross-sectional view of the screw driver of FIG. 34A; andFIG. 34C is a cross sectional view of the screw driver of FIG. 31 in alocked configuration;

FIG. 35 is a detail view of the screw driver of FIG. 31 coupled to afixation element;

FIG. 36A is a cross-sectional view through the distal end of the colletof the screw driver of FIG. 31; and FIG. 36B is a cross-sectional viewthrough the distal end of the collet of the screw driver of FIG. 31 andthe fixation element of FIG. 35;

FIG. 37A is a cross-sectional view through an alternate embodiment of ascrew driver; and FIG. 37B is a detail view of the distal end of thescrew driver of FIG. 37A coupled to a fixation element;

FIG. 38A is a side view of the screw driver of FIG. 37B; FIG. 38B is across-sectional view of the screw driver of FIG. 38A in a lockedconfiguration with a fixation element; FIG. 38C is a detailcross-sectional view of the distal end of the screw driver of FIG. 38B;FIG. 38D is a is a detail cross-sectional view of the distal end of thescrew driver of FIG. 38D; cross-sectional view of the screw driver ofFIG. 38A in an unlocked configuration; and FIG. 38E

FIG. 39A is a perspective view of a base reamer; FIG. 39B is a side viewof the base reamer of FIG. 39A; and FIG. 39C is a cross-sectional viewof the base reamer of FIG. 39A;

FIG. 40A is a perspective view of a bases broach; FIG. 40B is a sideview of the base broach of FIG. 40A; FIG. 40C is a cross-sectional viewof the base broach of FIG. 40A; FIG. 40D is a detail view of the distalend of the base broach of FIG. 40A; and FIG. 40E is an end view of thebase broach of FIG. 40A;

FIG. 41 is a perspective view of a base inserter;

FIG. 42A is a perspective view of the base inserter of FIG. 41 coupledto a modular handle; FIG. 42B is a detail view of the distal tip of thebase inserter of FIG. 42A; FIG. 42C is a cross-sectional view of thebase inserter of FIG. 42A;

FIG. 43 is a perspective view of a superior implant inserter;

FIG. 44A is a front perspective view of a lockout tool; and FIG. 44B isa rear perspective view of the lockout tool of FIG. 44A;

FIG. 45 is a cross-sectional view of the lockout tool of FIG. 44;

FIG. 46A is a front perspective view of an inferior trial; FIG. 46B is arear perspective view of the inferior trial of FIG. 46A; and FIG. 46C isa bottom view of the inferior trial of FIG. 46A;

FIG. 47 is an exploded view of the inferior trial of FIG. 46;

FIG. 48A is a perspective view of an inferior inserter; and FIG. 48B isan exploded view of the inferior inserter of FIG. 48A;

FIG. 49A is a side view of the inferior inserter of FIG. 48; and FIG.49B is a cross-sectional view of the inferior inserter of FIG. 48;

FIG. 50 is an exploded view of an alternate embodiment of an inferiorinserter;

FIG. 51 is a posterior view of the base reamer of FIG. 39 passing over afixation element in a caudal vertebra;

FIG. 52 is a partial cross-sectional view of the base reamer, fixationelement, and vertebra of FIG. 51, cut along the longitudinal axis of thefixation element;

FIG. 53 is a posterior view of the base broach of FIG. 40 passing over afixation element in a caudal vertebra;

FIG. 54 is a partial cross-sectional view of the base broach, fixationelement, and vertebra of FIG. 53, cut along the longitudinal axis of thefixation element;

FIG. 55 is a posterior view of an implant base, coupled to the baseinserter and handle of FIG. 42, passing over a fixation element in acaudal vertebra;

FIG. 56 is a partial cross-sectional view of the implant base, baseinserter, handle, fixation element, and vertebra of FIG. 53, cut alongthe longitudinal axis of the fixation element;

FIG. 57A is a detail cross-sectional view of the implant base, baseinserter, handle, fixation element, and vertebra of FIG. 53, cutperpendicular to the longitudinal axis of the fixation element; and FIG.57B is a partial cross-sectional view of the implant base, baseinserter, handle, fixation element, and vertebra of FIG. 53, cutperpendicular to the longitudinal axis of the fixation element;

FIG. 58 is a posterior view of a superior implant, coupled to thesuperior implant inserter of FIG. 43, passing over the base inserter ofFIG. 41 coupled to an implant base in a vertebra;

FIG. 59 is a posterior view of the superior implant, superior implantinserter, base inserter, and implant base of FIG. 58, with the superiorimplant engaging the implant base;

FIG. 60 is a lateral view of the superior implant, superior implantinserter, base inserter, and implant base of FIG. 59;

FIG. 61 is a posterior view of the superior implant, superior implantinserter, base inserter, and implant base of FIG. 59 and a contralateralset of minor image components;

FIG. 62 is a posterior view of the superior implant, superior implantinserter, base inserter, and implant base of FIG. 59 and the lockouttool of FIGS. 44-45;

FIG. 63 is a perspective view of the superior implant, superior implantinserter, base inserter, implant base and lockout tool of FIG. 62,showing the lockout tool before actuation;

FIG. 64 is a perspective view of the superior implant, superior implantinserter, base inserter, implant base and lockout tool of FIG. 62,showing the lockout tool during actuation;

FIG. 65 is a posterior view of the superior implant and fixationassembly of FIG. 23 in a caudal vertebra, the base inserter of FIG. 41coupled to an implant base in a cephalad vertebra, and an inferiortrial, coupled to the inferior inserter of FIG. 50, passing over thebase inserter;

FIG. 66 is a posterior detail view of the items shown in FIG. 65;

FIG. 67 is a posterior detail view of the items shown in FIG. 65, withthe inferior trial coupled to the superior implant;

FIG. 68 is a posterior detail view of the superior implant and fixationassembly of FIG. 23 in a caudal vertebra, the base inserter of FIG. 41coupled to an implant base in a cephalad vertebra, and an inferiorimplant, coupled to the inferior inserter of FIG. 50, with the inferiorimplant engaging the implant base;

FIG. 69 is a posterior detail view showing a crosslinker engaged withone of a bilateral pair of inferior implants fixed to a cephaladvertebra;

FIG. 70 is a posterior detail view showing bilateral counter torquetools stabilizing split clamps at the ends of the crosslink of FIG. 69.

DETAILED DESCRIPTION

The present invention advances the state of the art by providing systemsand methods that can be used to replace natural vertebral facet jointswith implantable artificial facet joint prostheses in a manner thatprovides a high degree of implant adjustability, simplicity, and ease ofuse.

In this application, “polyaxial” rotation is rotation that can occurabout at least two axes that are not parallel to each other. “Lock-out”between two or more component parts refers to a state in which movementof any component part is prevented by frictional, compression,expansion, or other forces. A “taper-lock connector” refers to anylocking mechanism that uses a taper to effect locking.

Referring to FIG. 1, a perspective view depicts a portion of a spineincluding a first vertebra 2 and a second vertebra 4. Sagittal plane 3is shown bisecting the vertebrae 2 and 4 into generally symmetric leftand right portions. A system 10 of bi-lateral facet joint replacementsjoined by a crosslink rod 108 passing through a spinous process 6 ofvertebra 4 is implanted in the vertebrae 2, 4. On the left side of thevertebrae 2, 4, an inferior facet joint implant 100 is secured to afixation assembly 300 implanted in vertebra 4, and a superior facetjoint implant 200 is secured to a fixation assembly 300 implanted invertebra 2. On the right side of the vertebrae, an inferior facet jointimplant 101 is secured to a fixation assembly 300 implanted in vertebra4, and a superior facet joint implant 201 is secured to a fixationassembly 300 implanted in vertebra 2. It is appreciated that the facetjoint replacement implants described herein may each be configured in a“right” or a “left” configuration to be implanted on the right or leftlateral side of the vertebrae. However, only one (right or left)configuration will be described, and it is assumed that the other (rightor left) configuration is a minor-image of the one described. It is alsoappreciated that the implants described herein may be implantedbi-laterally as in FIG. 1, or unilaterally, if desired.

Referring to FIG. 2, a perspective view depicts polyaxially adjustableleft inferior facet joint implant 100. Inferior facet joint implant 100comprises an inferior articular body 102, an inferior strut 104, and anattachment mechanism 106 which adjustably secures the articular body tothe inferior strut 104. The attachment mechanism 106 has an adjustableconfiguration in which the inferior articular body 102 can rotaterelative to the inferior strut 104 about three orthogonal axes, and ithas a locked configuration in which the inferior articular body 102 isrigidly secured to inferior strut 104. A crosslink rod 108 mayoptionally be secured to the implant 100 by a split clamp 110. Theattachment mechanism 106 may be actuated to simultaneously lock thecrosslink rod 108 in the split clamp 110 as the inferior articular body102 is locked to the inferior strut 104. A clamp axis 111 extendslongitudinally through the attachment mechanism. A strut axis 105extends longitudinally along the inferior strut 104.

Referring to FIG. 3, an exploded perspective view illustrates thecomponent parts which may comprise the left inferior facet joint implant100. The inferior articular body 102 is shell-like and has asubstantially concave interior cavity 112 which is defined by aninterior wall 114. A first chamfered opening 116 and a second chamferedopening 118 in the inferior articular body 102 create a passagewaythrough which a portion of the inferior strut may fit when the implantis assembled. An attachment post opening 120, which may also bechamfered, is situated orthogonal to the first and second chamferedopenings 116, 118. The chamfered openings may provide additional rangeof motion between the inferior articular body and the inferior strut 104as the inferior articular body 102 is polyaxially adjusted prior tolocking down. An inferior articular surface 122 is located on theexterior of the inferior articular body 102, and is shaped to replace anatural inferior articular surface of a vertebra. Inferior facet implant100 may be implanted in conjunction with a superior facet implant,wherein the inferior articular surface 122 articulates with anartificial superior facet articular surface. Alternately, inferior facetimplant 100 may be implanted such that the inferior articular surface122 articulates with a natural superior facet articular surface. In bothcases, the articulation between inferior and superior articular surfacespreserves a level of natural spinal motion.

FIG. 4 displays the attachment mechanism 106 in a cross-sectional view.The attachment mechanism 106 is configured to provide polyaxialadjustability between the inferior articular surface 122 and theinferior strut 104. Once the desired orientation of the articularsurface 122 relative to the inferior strut 104 is reached, theattachment mechanism 106 may be locked down, securing the articularsurface to the inferior strut. Referring to FIGS. 3 and 4, theattachment mechanism comprises a locking member which is a threadedconical expander 126, an expandable member which is a split shell 128,the split clamp 110, and a nut 130. An alternative embodiment of anattachment mechanism may exclude the split clamp 110.

The split shell 128 has a circular neck portion 132 through which passesa bore 134. The bore opening is surrounded by a radial spline 136.Adjacent to the neck portion 132 is a spherical portion 138 whichcomprises two expandable lobes 140, 142. An interior surface 143 of thelobes 140, 142 may be tapered. The present embodiment of the inventionincludes two lobes, however it is appreciated that more lobes may beincluded, or other expandable portions, in other embodiments. The splitshell 128 fits over the conical expander 126 such that a threaded post146 of the conical expander 126 passes through the bore 134. Anexpansion portion 148 of the conical expander 126 is forked and has twoopposing flanges 150, 152 which are shaped to fit around and grip theinferior strut 104. An inner wall 153 of the flanges is curved to fitaround the inferior strut 104, and the outer walls 154, 156 are tapered.

The split ring clamp 110 comprises an inner ring 160, an outer ring 162and a collar 164 which joins the inner and outer rings. The collar 164is shaped to fit around and grip the crosslink rod 108. The split ringclamp 110 is configured such that when the inner and outer rings 160,162 are compressed together, a diameter of the collar 164 decreases andthe collar can tighten around and secure the crosslink rod. The surfaceof an exterior side of the inner ring 160 is a radial spline 166, whichis shaped to engage with the radial spline 136 on the split shell 128.

When assembled, the split shell 128 fits over the conical expander 126,and the two parts fit within the inferior articular body 102 such thatthe interior cavity 112 houses the expansion portion 148 of the conicalexpander 126 nested inside the spherical portion 138 of the split shell128. The conical expander 126, split shell 128 and inferior articularbody 102 are oriented so that in general the flanges 150, 152 areadjacent to the lobes 140, 142, and the lobes are adjacent to theinterior wall 114 of the interior cavity 112. A strut post 184 of theinferior strut 104 fits between the flanges 150, 152 of the conicalexpander 126.

The split ring clamp 110 fits over the threaded post 146 of the conicalexpander 126 so that the radial spline 166 of the split clamp meets theradial spline 136 of the split shell 128. The crosslink rod 108 extendsthrough the collar 164 of the split clamp. The nut 130 is threaded ontothe threaded post 146 of the conical expander 126.

Until the attachment mechanism 106 is locked down by actuating the nut130, the implant is adjustable in multiple ways. The crosslink rod 108has relative angular freedom of motion about the clamp axis 111 and theinferior strut axis 105. The position of the crosslink rod 108 relativeto the split clamp 110 may be adjusted such that a relatively longer orshorter length of the crosslink rod 108 extends through the clamp. Thisprovides an opportunity to select the best fit to the patient's anatomyand the specific vertebral level being treated. Similarly, the positionof the inferior strut 104 may be adjusted relative to the inferiorarticular body 102 such that a relatively longer or shorter length ofthe inferior strut 104 extends through the flanges 150, 152 of theconical expander 126. Also, the inferior strut 104 has relative angularfreedom of motion about the clamp axis 111. The inferior articular body102 may be polyaxially rotated about the conical expander 126 and thesplit shell 128. The adjustments provide relative rotation between theinferior articulation surface 122 and the inferior strut 104 about threeorthogonal axes. In addition, prior to lockdown, relative translationbetween the inferior strut 104, the inferior articulation surface 122,and the crosslink rod 108 is permitted.

The attachment mechanism 106 is locked down by actuating, or turning thenut 130. As the nut 130 is turned and its threads engage the threadedpost 146, the conical expander 126 is urged “upward” through the nut130, while the outer ring 162 of the split clamp 110 is urged “downward”toward the inner ring 160. As the conical expander 126 moves, theflanges 150, 152 push against the lobes 140, 142 of the split shell 128,and in turn the lobes expand and push against the interior wall 114 ofthe interior cavity 112. Simultaneously, the flanges 150, 152 arecompressed around the inferior strut 104. Similarly, the collar 164 ofthe split clamp 110 is compressed around the crosslink rod 108 as theinner 160 and outer 162 rings of the clamp are urged together. The nut130 may be actuated until the resulting internal compression preventsany further motion, and the mechanism 106 is locked down.

The inferior implant 100 may be delivered in an assembled, but notlocked down, configuration. The crosslink rod 108 may be included in theassembly, provided separately, or excluded. The inferior implant 100 maybe delivered in combination with a superior implant, in which a clip orother temporary fastener holds the inferior articular surface to asuperior articular surface of the superior implant.

FIG. 5 presents an alternative embodiment of an inferior articular body470, which may be available pre-packaged temporarily attached to acoupler, or clip 550 with a plug 570. Alternatively, a gripping tool(not shown) may be used to hold the inferior articular body 470. It canbe appreciated that any of the various embodiments of the inferiorarticular body disclosed may be adapted for use with the clip 550 andplug 570. The inferior articular body 470 may be assembled to anattachment mechanism and inferior strut (not shown) in a manner similarto that described above with regard to other inferior implantembodiments.

FIG. 6 is a perspective view of the clip 550 and the plug 570. Clip 550comprises a clip body 552, a handle 554, and two pairs of pins whichextend substantially orthogonally from the body: a pair of superior pins556 and a pair of inferior pins 558. The inferior pins 558 arecannulated, each having a bore 560 which extends the length of the pin558, from the body 552 to a split end 562. Each split end 562 includesat least one slot 564 which extends partially along the length of thepin 558, and a protruding flange 566. The inferior pins 558 are shapedto receive an inferior facet joint implant, and the superior pins 556are shaped to receive a superior facet joint implant.

The plug 570 comprises a handle 571 and two prongs 572 which are sizedto extend through the bores 560 of the inferior pins 558 of the clip550. When the plug 570 is inserted fully into the inferior pins 558, theprongs 572 urge apart the split ends 562 from a narrow firstconfiguration to an expanded second configuration in which the slots 564are widened, and the flanges 566 on each pin are farther apart. When theplug 570 is removed, the split ends 562 return from the expanded secondconfiguration to the narrow first configuration.

Returning to FIG. 5, the inferior articular body 470 is shown coupledwith the clip 550 and the plug 570. The inferior pins 558 extend throughtubes 472 formed on the inferior implant 470, such that the split ends562 and flanges 566 emerge outside of the tubes. The plug 570 is fullyinserted through the clip bores 560, and therefore the prongs 574 keepthe split ends in the expanded second configuration. In the expandedsecond configuration, the widened flanges 566 cause the diameter of thesplit ends 562 to be greater than the diameter of the tubes 472,preventing the clip 550 from being withdrawn from the inferior articularbody 470. Thus held by the clip 550, the inferior articular body 470,with or without other attached components such as an inferior strut, maybe clipped to a superior implant.

Referring to FIG. 7A, an alternate embodiment of a coupling clip isshown. Clip 1200 is of one-piece construction, and is shaped to couplean inferior facet replacement implant such as inferior implant 100(FIG. 1) with a superior facet replacement implant such as superiorimplant 210 (FIG. 23). Clip 1200 may retain the implants such that theinferior and superior articulation surfaces are held at a desiredrelative position. A portion of the clip 1200 is deformable and may beflexed to detach the clip from at least one of the implants.

Clip 1200 comprises a first end 1202 and a second end 1204, and the endsare linked by a connecting portion 1206. First end 1202 comprises arigid shoulder 1208, and at opposing ends of the rigid shoulder 1208 area tab 1210 and a post 1212. The tab 1210 and post 1212 are also rigid,and are shaped to couple with and align the inferior and superiorimplants. A recess 1220 is located on the shoulder 1208. Similarly,second end 1204 comprises a rigid shoulder 1214, tab 1216, post 1218,and recess 1222. Tabs 1210, 1216 are shaped to receive an inferior facetjoint implant, and posts 1212, 1218 are shaped to receive a superiorfacet joint implant. Connecting portion 1206 is deformable, and when itis flexed, first end 1202 rotates about the axis of post 1212, andsecond end 1204 rotates about the axis of post 1218, such that tabs1210, 1216 are urged apart.

FIG. 7B is a perspective view of clip 1200 coupled to an inferior facetjoint implant 1230. Inferior facet joint implant 1230 is similar toinferior implant 100 seen in FIG. 2, but includes an alternativeinferior articular body 1232. Inferior facet joint implant 1230comprises inferior articular body 1232, conical expander 126, splitshell 128, split clamp 110, top nut 130, inferior strut 104, and splitsphere 356 which may be captured in the ring 182 of the inferior strut.Inferior articular body 1232 comprises an inferior articular surface1234 and a pair of slots 1236 which are shaped to receive the tabs 1210,1216 of the clip 1200. Inferior facet joint implant 1230 may bedelivered coupled to clip 1200. Packaging (not shown) may be shaped toprevent connecting portion 1206 from flexing, and to keep posts 1212,1218 in a fixed position.

FIGS. 8 and 9 present an alternative embodiment of an inferior implant400 with an alternative embodiment of an inferior articular body 402.This embodiment may differ from inferior articular body 102 in that itcomprises a gripping feature 404 between the attachment opening 120 andthe inferior articular surface 122. The gripping feature 404 comprisesan elongated slot 406 with an angled hole 408 cut into each end of theslot 406 (FIG. 9). The two holes 408 may diverge so that the grippingfeature 404 is undercut at each end of the slot 406. Alternatively, thegripping feature 404 may comprise another undercut configuration, suchas a dovetail or a keyseat.

Referring to FIG. 10, another alternate embodiment of a coupling clip isshown. Clip 410 comprises a clip body 412, an instrument socket 414, atab 420, a pair of pins 416, and a pair of prongs 418. The pins 416 areshaped to engage a superior facet joint implant and the prongs 418 areshaped to engage an inferior facet joint implant. The pins 416 may becylindrical and they may or may not have a constant diameter over theirentire length. The prongs 418 may flare away from each other or presenta dovetail or flanged configuration corresponding to the configurationof the gripping feature on the inferior facet joint implant. The pins416 and prongs 418 project orthogonally from a distal side of the clipbody 412, and the tab 420 projects orthogonally from a proximal side ofthe clip body 412. The socket 414 is located between the prongs 418 andmay be oriented at an angle to the clip body 412. A first slot 422 cutsthrough the clip body 412 so that the pins 416 are disposed on one sideof the slot 422 and the prongs 418 are disposed on the other side. Theslot 422 extends through a portion of the tab 420 adjacent to the clipbody 412. The slot 422 enables the clip 410 to flex so that the prongs418 can move toward or away from the pins 416. A second slot 424 isoriented perpendicular to the first slot 422, and cuts through theportion of the tab 420 that bears the prongs 418 and the socket 414, sothat the slot 424 is substantially centered with respect to the prongs418 and the socket 414. The slot 424 enables the clip 410 to flex sothat the prongs 418 can move toward or away from each other and thesocket 414 can increase or decrease in width.

Referring to FIG. 11, inferior strut 104 is shown coupled to fixationassembly 300, which may also be termed an attachment mechanism. Theinferior strut 104 is generally elongated in configuration, with acentral portion 180, a first end which is a ring 182, and a second endwhich is a strut post 184. The ring 182 may be a generally circularfeature with a center point and opposed end faces which aresubstantially planar and parallel. The ring 182 may be set at an anglerelative to the central portion 180 and the strut post 184. The strutpost 184 may be a generally cylindrical feature with a longitudinalcenter axis. The strut post 184 may be at an angle relative to thecentral portion 180 and the ring 182; also the central portion 180 maybe straight, bent or curved.

A kit of inferior implants may be provided, wherein each inferiorimplant in the kit is a different size or shape so that a particularinferior implant may be selected for implantation at a certain operativesite. U.S. patent application Ser. No. 12/240,320, which is incorporatedherein by reference in its entirety, describes such a kit of inferiorimplants in terms of physical dimensions which may vary independentlyamong the various inferior implants in the kit.

Some of the physical dimensions that may change between the differentsizes of inferior implants are an X2 offset, a Y2 offset, and a Z2offset. These dimension may be used to describe the location of a centerpoint C1 of the inferior articulation surface with respect to localvertebral landmarks, such as a pedicle saddle point or pedicle axis, orstandard anatomical reference planes, such as the sagittal plane 3. Itcan be appreciated that the same dimensions may be measured on one ormore intact natural vertebrae in order to develop inferior implants thataccurately fit a majority of the patient population.

The pedicle axis may be the same as the longitudinal axis of fixationmember 302, or any other fixation member disclosed herein, afterimplantation into a pedicle. The pedicle axis may also be the axispassing along the center of a substantially tubular midportion of thepedicle, independent of any fixation member. The pedicle saddle point isfrequently equivalent to the entry point of a fixation member into thepedicle; it may also be defined as the intersection of the pedicle axisand the posterior bone surface lateral to the superior articular processof a vertebra.

Exemplary values for the foregoing dimensions will be provided below.Although the exemplary values relate primarily to L5 superior and L4inferior, they may apply to other combinations of vertebrae in the lowerback and/or the sacrum. One or more of these variables may changebetween the different inferior implant sizes.

For a particular inferior articular surface and its immediately adjacentpedicle, the center point C1 of the inferior articulation surface isdisplaced from the saddle point S2 by an X2 offset, a Y2 offset, and aZ2 offset. The direction of the Y2 offset is parallel to the pedicleaxis. The direction of the Y2 offset is generally, but not precisely,anterior to posterior. The direction of the X2 offsets is perpendicularto the Y2 offset. The direction of the X2 offset is generally, but notprecisely, lateral to medial with respect to the central axis of thepatient's spine. The direction of the Z2 offset is perpendicular to theY2 offset and the X2 offset. The direction of the Z2 offset is generallycephalad to caudal.

The X2 offset for the inferior implant can range from 0 mm to 20 mm.However, for the majority of patients, the X2 offset will range from 2mm to 16 mm. Therefore a family of inferior implants can be providedwith the X2 offset varying in increments of 2 mm. Thus, sets of inferiorimplants would be provided with X2 offset at 2 mm, 4 mm, 6 mm, 8 mm, 10mm, 12 mm, 14 mm, and 16 mm to cover the statistical range for themajority of the population of patients needing inferior implants.

The Y2 offset for the inferior implant can range from −15 mm to 5 mm.However, for the majority of patients, the Y2 offset will range from −12mm to 4 mm. Therefore a family of inferior implants can be provided withthe Y2 offset varying in increments of 2 mm. Thus, sets of inferiorimplants would be provided with Y2 offset at −12 mm, −10 mm, −8 mm, −6mm, −4 mm, −2 mm, 0 mm, 2 mm, and 4 mm to cover the statistical rangefor the majority of the population of patients needing inferiorimplants.

The Z2 offset for the inferior implant can range from 20 mm to 40 mm.However, for the majority of patients, the Z2 offset will range from 25mm to 31 mm. Therefore a family of inferior implants can be providedwith the Z2 offset varying in increments of 1 mm. Thus, sets of inferiorimplants would be provided with Z2 offset at 25 mm, 26 mm, 27 mm, 28 mm,29 mm, 30 mm, and 31 mm to cover the statistical range for the majorityof the population of patients needing inferior implants.

The parameters of the inferior implant may include at least twodimensions that vary among the members of the kit independently of eachother. Dimensions that vary independently of each other need not changeaccording to any established relationship between the dimensions, butinstead, one may change while the other remains the same between any twoprostheses of the kit. More specifically, the kit of inferior implantsmay comprise a plurality of inferior struts of different sizes andshapes, each of which may be provided pre-assembled with an inferiorarticular body, an attachment mechanism, and optionally a split sphere.As set forth previously, the relative orientation of the ring, centralportion, and strut post of the inferior strut may vary. In oneembodiment, the tip of the strut post may be offset from the centerpoint of the ring by one or more of the X2 offset, the Y2 offset, andthe Z2 offset.

Fixation assembly 300 is configured to be implanted in a pedicle of avertebra, and to be coupled to inferior implant 100 or another implant.The fixation assembly 300 provides for polyaxial adjustment of theimplant with respect to the fixation assembly 300, and comprises afixation member 302, a tapered base 304, a split sphere 306, and a topnut 308.

FIG. 12 is an exploded view of the inferior strut 104 and the fixationassembly 300. The fixation member 302, which may be a pedicle screw, hasa distal threaded bone engaging portion 310, a shaft 312, and a proximalthreaded attachment portion 314. The tapered base 304 is cannulatedthroughout, and has an inset bone-engaging portion 316, a flange 318,and a tapered portion 320. The inset portion 316 may be tapered toprovide compression to the surrounding bone, and may have a plurality offins 317 which prevent rotation of the base 304 in the bone. Inalternate embodiments of the invention, the inset portion 316 mayinclude teeth, studs, fins, or combinations thereof, or otheranti-rotation features, or no anti-rotation features. The taperedportion 320 may serve as an attachment portion, configured forattachment of an implant. At an open end of the tapered portion 320, atool engagement rim 322 includes a plurality of notches 324. Otherembodiments of the base may include threads or other features instead ofnotches configured to engage a tool. An inner wall 326 of the splitsphere 306 is sized to fit over the tapered portion 320 of the base 304,and includes a plurality of slits 328 which allow the sphere to beexpandable. The inner wall 326 of the split sphere 306 may also betapered. The top nut 308 has a threaded bore 332 and a flange 334 whichencircles the nut 308.

The fixation assembly 300 may be assembled from the components describedabove during implantation, or it may be delivered in a partiallyassembled state. For example, the split sphere 306 may be providedcaptive within the ring 182.

Prior to locking down the fixation assembly 300, the ring 182 may bepolyaxially adjusted around the split sphere 306 so that the inferiorstrut 104 attains a desired orientation. To lock down the desiredorientation, a compression lockout tool (not shown) engages the notches324 of the tool engagement rim 322 on the base 304. Other embodiments ofthe base may include a threaded tool engagement interface, configured toengage with a threaded lockout tool. The lockout tool providescompression on the split sphere 306, urging it farther onto the taperedportion 320 toward the flange 318. As the split sphere 306 moves downthe tapered portion 320, it expands to bind within the ring 182 of theinferior strut 104. Once all motion between the tapered portion 320,split sphere 306 and ring 182 is locked out, the lockout tool isremoved. The top nut 308 is threaded onto the threaded attachmentportion 314 of the fixation member 302, to retain the base 304, sphere306 and inferior strut 104 on the fixation member 302, and to furthersecure the inset portion 316 of the base 304 in the vertebra.Optionally, the base 304, split sphere 306, and inferior strut 104 maybe assembled and locked out independently of the fixation member 302,then dropped onto the fixation member 302 and retained with the top nut308. The inferior articular body 102 and the attachment mechanism 106may be secured to the inferior strut 104 before or after the inferiorstrut 104 is locked into position with the base 304 and split sphere306.

FIGS. 13-20 depict alternative embodiments of implant base members. Eachbase member comprises a tapered portion shaped to mate with anexpandable member, or collet that is tapered inside and substantiallyspherical outside, such as split sphere 306 or 356. The tapered surfacefacilitates a taper lock between the base and the collet (and inferioror superior implant), thereby locking out adjustability between theimplant and the base as described previously with regard to FIG. 12.Below the tapered portion may be a flange to prevent subsidence andprovide a stable surface against the adjacent bone, and to provideadditional surface area for bone ingrowth. In addition, a generallycylindrical bone-engaging portion of the base extends down into thepedicle of the vertebra. The bone-engaging portion, which may also betapered forming a conical shape, may have any number of fins or otherfeatures (3-7 in preferred embodiments) which may project into thesurrounding bone to resist rotation forces. Each base has a lumenextending throughout both the tapered portion and bone-engaging portionto fit over a pedicle screw or other fixation member. The lumen may becylindrical or may include a non-cylindrical indexing surface with oneor more flat sections, shaped to receive a hexagonal driver or a driverof another shape, including triangular, square, pentagonal, oroctagonal, among others. Additionally, each base may have engagementfeatures such as notches or threads which allow a tool or grippinginstrument to engage with and hold the base during implantation andlockout procedures. Implantation of each base may follow the sameprocedures as set forth previously for base 304. Bases with fins orother protruding anti-rotation features may require additional bonepreparation steps, such as broaching, to adequately prepare the bone forthe fins.

Each base member embodiment may differ in the number of fins thatradiate outward from the center axis to resist rotation. The length,width, and taper of fins or other anti-rotation features may vary. Otherembodiments of the implant base may have studs, pegs, or posts insteadof fins, or may have slots in the bone-engaging portion that extenddownward into the pedicle. Also, the flange and/or bone-engaging portionmay be coated with bone in-growth material, such as porous material orhydroxyapatite, among others. Additional embodiments may incorporatesawtooth fins to allow for self-guiding and/or self-cutting, thereforeeliminating a separate preparation step. It is appreciated that thebases disclosed herein may be used with the fixation assemblies alsodisclosed herein, or in other orthopedic applications employingbone-engaging fixation members.

The combination of a base member such as those disclosed herein with afixation member such as a pedicle screw may provide several advantageswhen compared to a pedicle screw alone. The contact area between thepedicle and the fixation assembly over which bending loads aredistributed will be increased, since the bone-engaging portion of eachbase provides a greater surface to bone contact area than a pediclescrew alone. According to Wolff's Law, a bone in a healthy person oranimal will adapt to the loads under which it is placed. If loading on aparticular bone increases, the bone will remodel itself over time tobecome stronger to resist that sort of loading. Increasing the bonecontact area through the use of a base member may therefore result instrengthening of a larger portion of the bone around the implantfixation assembly. Additionally, less load may be placed on the pediclescrew, which may result in decreased likelihood of loosening of thescrew over time.

FIG. 13A is a side view of a facet implant base member 850; FIG. 13B isan end view of the base 850; FIG. 13C is a perspective view of the base850; and FIG. 13D is cross-sectional view of the base 850. Base 850comprises a tapered portion 852 separated from a bone-engaging portion856 by a flange 854. A lumen 851 extends the length of the base, thelumen 851 is shaped to receive a fixation member such as 302, or apedicle screw, among others. A first end 858 includes several notches860 which are engagement features shaped to mate with a placement and/orlockout tool. In this embodiment, five evenly spaced fins 862 projectoutward from the bone-engaging portion 856. The fins 862 may preventrotation of the base 850 in the pedicle. A fillet 864 is located betweeneach fin and the adjacent fin and provides a transition between theflange 854 and the bone-engaging portion 856. In other embodiments ofthe base, there may be fewer or more fins, and the fins may be evenly orunevenly spaced, or paired, or grouped. The morphology of the fins mayvary; some fins may have sharp, well-defined edges while others may havemore rounded edges. The fins may taper between the flange and the distalend of the bone-engaging portion. Similarly, the sizes of the fillets864 may vary; a larger fillet will provide a less sharp, more continuoustransition between fins. Providing more gradual, less acute transitionsbetween features on the base may prevent the occurrence of low-loadareas where less bone in-growth might occur.

Referring to FIG. 14, an alternative embodiment of an implant basemember is shown. Implant base 870 has a tapered portion 872, a flange874 and a bone-engaging portion 876. A plurality of fins 878 extendoutward from the bone-engaging portion 876. The central lumen 871includes flat sections 873 interspersed with curved sections 875,allowing for engagement with a tool such as a pentagonal driver (notshown). The flat sections 873 may provide a practitioner with immediateorientation of the fins 878 relative to the bone screw with which thebase is coupled, as well as to broached slots in the bone. The curvedsections 875 have a diameter outside the dimensions of the flat sections873. The tapered portion includes threads 877 which may extendthroughout the tapered portion as shown or, in other embodiments, mayextend only partially through the tapered portion. The threads 877 areconfigured to engage with a placement and/or lockout tool, which mayprovide force to effect a taper lock between an implant and the base, asset forth previously.

Referring to FIG. 15, another alternative embodiment of an implant basemember is shown. Implant base 880 has a tapered portion 882, a flange884 and a bone-engaging portion 886. A plurality of fins 888 extendoutward from the bone-engaging portion 886. Each fin 888 is serratedwith several teeth 889, which may provide self-broaching of the boneduring implantation of the base.

Referring to FIG. 16, yet another alternative embodiment of an implantbase member is shown. Implant base 890 has a tapered portion 892, aflange 894 and a bone-engaging portion 896. A plurality of jagged fins898 extend outward from the bone-engaging portion 896. Each fin 898comprises a series of teeth 899 which may be graduated in size. Similarto implant base 880, the teeth may provide self-broaching duringimplantation, and may reduce the bone preparation needed prior toimplantation.

Referring to FIG. 17, another alternative embodiment of an implant basemember is shown. Implant base 900 comprises a tapered portion 902 and abone-engaging portion 904. A curved transitional area 906 connects thetapered portion and the bone-engaging portion. The transitional areaserves a similar function as the flange in other embodiments, preventingsubsidence of the implant. Two pegs 908, which may prevent rotation ofthe base, protrude outward from the bone-engaging portion 904.

Referring to FIG. 18, another alternative embodiment of an implant basemember is shown. Implant base 910 comprises a tapered portion 912 and abone-engaging portion 914. In this embodiment, the dish-shapedbone-engaging portion 914 has a greater diameter than the taperedportion 912. Bone-engaging portion 914 has a spherical bone-contactingsurface 915. The configuration of the bone-engaging portion 914 mayprevent subsidence of the implant, distribute the implant load over alarger surface area, and provide increased surface area for boneingrowth. A plurality of pegs 916 protrude from the bone-engagingportion 914 and may prevent rotation of the base. The pegs 916 arepositioned farther away from the central axis of the base abone-engaging portion 926. Bone-engaging portion 926 is tapered andincludes a plurality of holes 928 which open into the central cannulatedarea, and may allow additional bone ingrowth. 910, in comparison to theconfiguration of base 900 and pegs 908.

Referring to FIG. 19, another alternative embodiment of an implant basemember is shown. Implant base 920 comprises a tapered portion 922, aspherical transition portion 924, and a bone-engaging portion 926.Bone-engaging portion 926 is tapered and includes a plurality of holes928 which open into the central cannulated area, and may allowadditional bone ingrowth. Bone-engaging portion 926 may provide anarrower profile allowing for less disturbance of the pedicle duringpreparation and implantation.

Referring to FIG. 20, another alternative embodiment of an implant basemember is shown. Implant base 930 comprises a tapered portion 932, aspherical transition portion 934, and a tapered bone-engaging portion936.

FIG. 21 illustrates an alternate embodiment of a fixation element, orpedicle screw 1100. The pedicle screw 1100 has a distal threaded boneengaging portion 1168, a shaft 1138, and a proximal threaded attachmentportion 516. These features may be similar to, or identical to, thosedisclosed for fixation element 302. Pedicle screw 1100 also has aplurality of flats 1107 arranged around the proximal end. The flats 1107may extend along at least a portion of the proximal threaded attachmentportion 516 or the shaft 1138. In a preferred embodiment, the flats 1107extend along the majority of the shaft 1138 and the entire proximalthreaded attachment portion 516.

Referring to FIG. 22, the superior implant 200 is shown secured to thefixation assembly 300. The superior implant 200 may be monolithic andincludes a superior articulation surface 202 shaped to replace a naturalsuperior articular surface of a vertebra, a ring 204, and may include atleast one notch-like gripping feature 206. The superior implant 200 maybe secured to the fixation assembly 300 in the same method as describedpreviously for the inferior strut 104. The ring 204 of the superiorimplant 200 is locked in position relative to the split sphere 306 andthe base 304. The base 304, split sphere 306 and implant 200 may bedropped over an implanted fixation member 302, and the top nut 308secured on the fixation member 302 to retain the assembly. The superiorimplant 200 may be delivered in combination with an inferior implant100, and the superior articular surface 202 may be temporarily clippedto the inferior articular surface 122.

A kit of superior implants may be provided, wherein each superiorimplant in the kit is a different size or shape so that a particularsuperior implant may be selected for implantation at a certain operativesite. U.S. patent application Ser. No. 12/240,320, which is incorporatedherein by reference in its entirety, describes such a kit of superiorimplants in terms of physical dimensions which may vary independentlyamong the various superior implants in the kit.

Some of the physical dimensions that may change between the differentsizes of superior implants are an X1 offset, a Y1 offset and a facetangle. These dimensions may be used to describe the location andorientation of the superior articular surface of the superior implantwith respect to local vertebral landmarks, such as a pedicle saddlepoint or pedicle axis, or standard anatomical reference planes such asthe sagittal plane 3. It can be appreciated that the same dimensions maybe measured on one or more intact natural vertebrae in order to developsuperior implants that accurately fit a majority of the patientpopulation.

The pedicle axis may be the same as the longitudinal axis of fixationmember 302, or any other fixation member disclosed herein, afterimplantation into a pedicle. The pedicle axis may also be the axispassing along the center of a substantially tubular midportion of thepedicle, independent of any fixation member. The pedicle saddle point isfrequently equivalent to the entry point of a fixation member into thepedicle; it may also be defined as the intersection of the pedicle axisand the posterior bone surface lateral to the superior articular processof a vertebra.

Exemplary values for the foregoing dimensions will be provided below.Although the exemplary values relate primarily to L5 superior and L4inferior, they may apply to other combinations of vertebrae in the lowerback and/or the sacrum. One or more of these variables can changebetween the different superior implant sizes.

For a particular superior articular surface and its immediately adjacentpedicle, the point P1 is the most medial and anterior point on thesuperior articular surface. P1 is displaced from the saddle point S1 byan X1 offset and a Y1 offset. The direction of the Y1 offset is parallelto the pedicle axis. The direction of the X1 offset is perpendicular tothe direction of the Y1 offset. The direction of the X1 offset isgenerally, but not precisely, lateral to medial with respect to thecentral axis of the patient's spine.

The X1 offset for a superior implant can range from 5 mm to 30 mm.However, for the majority of patients, the X1 offset will range from 10mm to 20 mm. Therefore a family of superior implants can be providedwith the X1 offset varying in increments of 5 mm. Thus, sets of superiorimplants would be provided with X1 offset at 10 mm, 12 mm, 14 mm, 16 mm,18 mm, and 20 mm to cover the statistical range for the majority of thepopulation of patients needing superior implants.

The Y1 offset for a superior implant can range from 2 mm to 20 mm.However, for the majority of patients, the Y1 offset will range from 5mm to 15 mm. Therefore a family of superior implants can be providedwith the Y1 offset varying in increments of 2 mm. Thus, sets of superiorimplants would be provided with Y1 offset at 5 mm, 7 mm, 9 mm, 11 mm, 13mm, and 15 mm to cover the statistical range for the majority of thepopulation of patients needing superior implants.

The facet angle for a superior implant is the angle that the superiorarticular surface makes with respect to a plane perpendicular to thepedicle axis and passing through point P1. The facet angle can rangefrom 50° to 120°. However, for the majority of patients, the facet anglewill range from 60° to 100°. Therefore a family of superior implants canbe provided with the facet angle varying in increments of 5°. Thus, setsof superior implants would be provided with the facet angle at 60°, 65°,70°, 75°, 80°, 85°, 90°, 95°, and 100° to cover the statistical rangefor the majority of the population of patients needing superiorimplants.

The parameters of the superior implant may include at least twodimensions that vary among the members of the kit independently of eachother. Dimensions that vary independently of each other need not changeaccording to any established relationship between the dimensions, butinstead, one may change while the other remains the same between any twoprostheses of the kit.

FIG. 23 presents an alternative embodiment of a superior implant 210with an alternative embodiment of a polyaxially adjustable fixationassembly 350. FIG. 24 presents an exploded view of fixation assembly350, and FIG. 25 presents a cross-sectional post-assembly view of theassembly. With reference to FIGS. 23 and 28, superior implant 210 isdistinguished from superior implant 200 by holes 216 and 218 disposedbetween the ring and the articular surface. With reference to FIGS.23-25, fixation assembly 350 comprises a fixation member 352, a taperedbase 354, a flanged split sphere 356, a capture nut 358, and a top nut360. The cannulated tapered base 354 has an inset portion 362 which mayinclude anti-rotation features such as fins, teeth or studs. A taperedportion 364 has a threaded lumen 366. The split sphere 356 includes asplit flange 368 which encircles one open end of the sphere. The capturenut 358 has a threaded outer surface 370, while the top nut 360 has athreaded inner surface 372. Fixation assembly 350 may also be termed anattachment mechanism. It is appreciated that fixation assembly 350 maybe substituted for fixation assembly 300 in any fixation proceduredisclosed or depicted herein, and vice versa. Also, a combination offixation assemblies 300 and 350 may be used in an implant system.

Referring to FIG. 26, a perspective view shows the inferior articularbody 470 attached to a clip 550. A direction arrow 580 indicates thedirection in which the articular body and clip may be moved to alignthem with a superior implant 211. The superior implant 211 may beimplanted in a pedicle via fixation assembly 350 prior to alignment withthe inferior articular body 470. Using the handle 554, the clip may bemoved until the superior pins 556 fit into openings 582 on the superiorimplant 211. Alternatively, clip 550 and inferior articular body 470 maybe joined with an inferior strut (not shown) and with superior implant211 into an assembly, and the assembly moved onto fixation members 352implanted in the pedicles.

As seen in FIG. 27, when the pins 556 are fully inserted into theopenings 582, inferior articulation surface 474 is aligned with superiorarticulation surface 584 in a preferred orientation. At this point, anappropriately sized and configured inferior strut (not shown) may bechosen. The orientation of the inferior strut may be adjusted beforebeing locked down to a fixation member. Additionally, a crosslink rod(not shown) may be added and locked down as the attachment mechanism islocked down. To remove the clip 550, first the plug 570 is removed,allowing the split ends 562 to return to the first narrow configurationand making them narrow enough to be withdrawn through the tubes 472.Then the clip 550 may be removed.

Referring to FIG. 28, clip 1200 and implant 1230 are shown gripped by adelivery tool 1300. Additionally, superior facet implant 210 is showncoupled to fixation assembly 350. The delivery tool 1300 compriseshandles (not shown), a shaft 1302, a hook 1304 which may be actuated togrip and release the clip 1200, and a pair of pegs 1306, 1308. Uponremoval of the packaging described above, the delivery tool 1300 may beconnected to the clip 1200 via the hook 1304 which hooks on theconnection portion 1206, and the pegs 1306, 1308 which protrude into therecesses 1220, 1222. The spacing of the pegs keeps the posts 1212, 1218of the clip 1200 in a proper position for coupling with the superiorimplant 210. The hook 1304 may prevent premature flexure of theconnection portion 1206. The delivery tool 1300 may be manipulated toposition the clip 1200 and implant 1230 such that the posts 1212, 1218fit into the holes 216, 218 on the superior implant, thus properlyaligning the inferior 1234 and superior 214 articulation surfacesrelative to one another.

Referring to FIG. 29, a flexing tool 1320 is shown coupled to theconnecting portion 1206 of the clip 1200. Flexing tool 1320 is co-axial,and comprises handles (not seen), a shaft 1322, and two grippingfeatures 1324, 1326. The gripping features 1324, 1326 are shaped andpositioned to grip two locations on the connecting portion 1206. Theflexing tool 1320 may be activated to move the gripping features 1324,1326 relative to one another such that the connecting portion 1206 isflexed.

Referring to FIG. 30, inferior articular body 402 is shown coupled tosuperior implant 210 by clip 410. An inferior inserter 1800 is alsocoupled to the clip 410. Optionally, the inferior articular body 402 maybe assembled to other components of the inferior facet joint implant 400(FIG. 8). A split sphere 306 or 356 may be provided with the inferiorimplant 400 or the superior implant 210. Furthermore, the superiorimplant 210 may already be locked to a fixation assembly implanted in apedicle. However, these additional components are not shown in FIG. 30for clarity. Inferior articular body 402 is coupled to superior implant210 by clip 410 in a manner similar to that described for inferiorarticular body 470, clip 550, and superior implant 211 (FIG. 26) andinferior articular body 1230, clip 1200, and superior implant 210 (FIG.28). The inferior inserter 1800 may be used to position the clip 410 andinferior articular body 402 so that the prongs 416 of clip 410 engagethe holes 216 and 218 of the superior implant 210 so that the inferiorarticulation surface 122 is properly aligned to the superiorarticulation surface 214.

The coupling clips disclosed herein may be made in a variety of sizes,and with varied dimensions, to fit implants configured for differentvertebral levels. Other embodiments of clips may include differentdeformable retention features, different alignment features, and/ordifferent features shaped to receive the superior and inferior implants.Coupling clips without deformable features or plugs, and/or with otherattachment features are contemplated within the scope of the invention.In addition, trial clips in a variety of sizes and configurations may beprovided, to allow the practitioner to choose the correct size orconfiguration of implant. Trial clips may include integrated superiorand/or inferior implant trial components. A trial clip and implant maybe used to select the proper length of inferior strut to match an offsetdistance between the vertebrae. Specifically, fixation members and basemembers may be secured in adjacent vertebrae, and a succession oftrials, each comprising a clip retaining an inferior and optionally asuperior implant may be positioned on the bases, until the proper lengthof inferior strut is determined. Then the sterile package containing theproper choice of clip and implants may be opened and the appropriateclip and implants secured to the base members. Use of the trialsprevents practitioners from unnecessarily opening more than one sterilepackage of implants to determine a correct fit.

The facet joint replacement system 10 described above, and alternateembodiments thereof, may be implanted using a set of surgicalinstruments. At least some of the surgical instruments may bespecifically designed to facilitate implantation of one or more implantembodiments disclosed herein. Selected surgical instruments that mayfacilitate implantation of one or more embodiments of the facet jointreplacement system will now be described.

FIGS. 31-36 illustrate a first embodiment of a pedicle screw driver1130. The screw driver 1130 comprises an outer sleeve 1101, an innershaft 1102, a handle 1111, a lever 1110, a coupling element 1121, and atorque fitting 1104.

The outer sleeve 1101 is generally tubular and may be windowed. Theinner surface of the outer sleeve 1101 may have one or more tabs 1105near the distal end 1106. The tabs 1105 may be formed on a separatedistal tip portion which is subsequently affixed to the remainingportion of outer sleeve 1101, as is shown in FIGS. 31-36, or the tabs1105 may be formed as separate parts which are affixed to a unitaryouter sleeve 1101. The tabs 1105 may also be integrally formed with theouter sleeve 1101. The distal end 1106 of the outer sleeve 1101 mayoptionally comprise a replaceable burr or reamer with end cutting flutesor side cutting flutes, or both. End cutting flutes, if present, mayextend only partway from the outer diameter of outer sleeve 1101 towardthe inner surface so that a non-fluted annular region is present.

The inner shaft 1102 slides within the outer sleeve 1101, and is held ina fixed rotational alignment to the outer sleeve 1101, as will bedescribed below. The inner shaft 1102 has a collet 1112 on the distalend, as is best seen in FIGS. 31 and 33-35. The collet 1112 comprises acenter bore 1113 surrounded by a plurality of flexible prongs 1103separated by slots 1114. The center bore 1113 may be fabricated with aprecisely controlled predetermined depth from the open end of the collet1112. In the free state, i.e., when subject to no external forces, theprongs 1103 flare toward the open end of the collet 1112. When thecollet 1112 slides within the distal end 1106 of outer sleeve 1101, theprongs 1103 are compressed toward the center bore 1113 by the innersurface of the outer sleeve 1101. The one or more tabs 1105, if present,slide into one or more corresponding slots 1114 in the collet 1112 tofix the rotational alignment of the collet 1112 to the outer sleeve1101. One or more of the inner walls 1115 of the prongs 1103 may beflattened so that the center bore 1113 is non-circular or polygonal incross section.

The handle 1111 is rigidly fixed to the proximal end of the outer sleeve1101, and is generally tubular. The ends of handle 1111 may be reducedin diameter to blend with the outer diameter of the outer sleeve 1101.The handle 1111 may have a slot 1118 through which the lever 1110protrudes.

The lever 1110 is pivotally attached to the handle 1111 by pins 1122 andto the coupling element 1121 by pin 1119. In the embodiment shown, thelever 1110 protrudes through slot 1118 in the handle 1111. The lever1110 pivots between a first position, in which the lever 1110 liesgenerally flat against the handle 1111, and a second position, in whichthe free end of the lever 1110 lifts away from the handle 1111. Thecoupling element 1121 comprises a curved bar which is pivotally attachedto the inner shaft 1102 by pin 1120. Thus, the lever 1110, couplingelement 1121, and inner shaft 1102 form a mechanical linkage 1124 whichis pinned to handle 1111 by pins 1122. The linkage 1124 turns rotationalmotion of the lever 1110 into linear translation of the inner shaft 1102within the outer sleeve 1101. The linkage 1124 also holds inner shaft1102 in a fixed rotational alignment to the outer sleeve 1101.

The torque fitting 1104 is rigidly fixed to the proximal end of thehandle 1111. In the embodiment shown, the torque fitting 1104 is a shaft1126 terminating in a square tip 1128 suitable for connection to amodular handle or power driver (not shown). However, other torquefittings are contemplated, such as a hexagonal tip, threads, or otherfittings as are known in the art. The handle 1111 itself may serve as amanual torque fitting 1104.

The outer sleeve 1101 and inner shaft 1102 of the screw driver 1130cooperate to form a screw coupling 1116 that releasably couples thescrew driver 1130 to a fixation element such as pedicle screw 1100 (FIG.21). In the embodiment illustrated in FIGS. 31-36, the screw coupling1116 is formed by the collet 1112 at the distal end of the inner shaft1102 and the distal end 1106 of the outer sleeve 1101 adjacent to thecollet 1112. The distal end 1106 of outer sleeve 1101 forms a socket1117 around the collet 1112, and the center bore 1113 of collet 1112forms a socket around the pedicle screw 1100. The screw coupling 1116has an unlocked configuration, in which the pedicle screw 1100 and thescrew driver 1130 are separable. The screw coupling 1116 also has alocked configuration, in which the pedicle screw 1100 and the screwdriver 1130 are inseparable. Furthermore, in the locked configuration,the screw coupling 1116 transmits torque from the screw driver 1130 tothe pedicle screw 1100 in order to thread the pedicle screw 1100 into apedicle or other part of a bone.

When the free end of the lever 1110 is lifted away from the handle 1111,the lever 1110 rotates about pins 1122. A first end 1132 of couplingelement 1121 also rotates about pins 1122, because coupling element 1121is pivotally attached to the lever 1110 by pin 1119. As the first end1132 of coupling element 1121 rotates, it moves toward the distal end1106 of the outer sleeve 1101; it also pushes a second end 1134 ofcoupling element 1121 toward the distal end 1106 of the outer sleeve1101. A proximal end 1136 of the inner shaft 1102 is also pushed towardthe distal end of the screw driver 1130, because it is pivotallyattached to the second end 1134 of the coupling element 1121 by pin1120. The curved shape of coupling element 1121 allows it to flex, orbehave as a spring, in response to the applied forces on the first end1132 and any resisting forces on the second end 1134. Inner shaft 1102is only capable of linear translation within outer sleeve 1101, due tothe constraints imposed by outer sleeve 1101, handle 1111, lever 1110,and coupling element 1121. Thus, when the free end of the lever 1110 islifted away from the handle 1111, the proximal end 1136 of the innershaft translates toward the distal end 1106 of the outer sleeve 1101such that at least a portion of the distal collet 1112 protrudes pastthe distal end 1106 of the outer sleeve 1101. In this position, theinner surface of outer sleeve 1101 does not touch the collet 1112, sothe prongs 1103 flare toward the open end of the collet 1112. Thisconfiguration of the screw driver 1130 is called the unlockedconfiguration because the collet 1112 is unconstrained by the outersleeve 1101 and the prongs 1103 flare open to receive the pedicle screw1100 in the center bore 1113, as will be described presently. Thus, theunlocked configuration of the screw driver 1130 corresponds to theunlocked configuration of the screw coupling 1116.

When the lever 1110 is rotated to lie generally flat against the handle1111, the first end 1132 of coupling element 1121 moves away from thedistal end 1106 of the outer sleeve 1101; it also pulls the second end1134 of coupling element 1121 away from the distal end 1106 of the outersleeve 1101. The proximal end 1136 of the inner shaft 1102 is alsopulled away from the distal end 1106 of the outer sleeve 1101. Thecurved shape of coupling element 1121 allows it to flex, or behave as aspring, in response to the applied forces on the first end 1132 and anyresisting forces on the second end 1134. Thus, when the lever 1110 liesgenerally flat against the handle 1111, the proximal end 1136 of theinner shaft 1102 translates away from the distal end 1106 of the outersleeve 1101 such that a substantial portion of the distal collet 1112 isretracted within the distal end 1106 of the outer sleeve 1101. In apreferred embodiment, the open end of the collet 1112 is preciselyaligned with the distal end 1106 of the outer sleeve 1101 such that thecenter bore 1113 is at a precisely controlled predetermined depth fromthe distal end 1106 of the outer sleeve 1101. In this position, theinner surface of outer sleeve 1101 contacts the collet 1112, compressingthe prongs 1103 toward the center bore 1113 as described above. The oneor more tabs 1105, if present, engage one or more corresponding slots1114 in the collet 1112 as described above. This configuration of thescrew driver 1130 is called the locked configuration because the collet1112 is compressed by the outer sleeve 1101 so that the prongs 1103 willgrasp a pedicle screw 1100 in the center bore 1113, as will be describedbelow. Thus, the locked configuration of the screw driver 1130corresponds to the locked configuration of the screw coupling 1116.

FIGS. 37A-38E illustrate a second embodiment of a pedicle screw driver1140. In this embodiment, the screw driver 1140 comprises an outersleeve 1142 and an inner shaft 1144 which differ from the previousembodiment, as well as a handle 1146, a lever 1148, a coupling element1150, and a torque fitting 1152 which may be similar or identical tothose described for screw driver 1130.

The outer sleeve 1142 is generally tubular and may be windowed. Theinner surface of the outer sleeve 1142 has internal threads extendingfrom a distal end 1164 along at least a portion of the length of theouter sleeve 1142. The internal threads are complementary to theexternal threads on the proximal attachment portion 516 of pedicle screw1100. In other regards, the outer sleeve 1142 may be similar oridentical to the outer sleeve 1101 described for screw driver 1130. Thedistal end 1164 of the outer sleeve 1142 may optionally comprise areplaceable bun or reamer, as described for screw driver 1130.

The inner shaft 1144 slides within the outer sleeve 1142, and is held ina fixed rotational alignment to the outer sleeve 1142. The inner shaft1144 terminates in a blunt distal end 1160. In other regards, the innershaft 1144 may be similar or identical to the inner shaft 1102 describedfor the previous embodiment.

The handle 1146, lever 1148, and coupling element 1150 depicted forscrew driver 1140 may differ in appearance from, but may retain the samefunction as, those described for screw driver 1130. In this embodiment,handle 1146 serves as a manual torque fitting 1152.

The outer sleeve 1142 and inner shaft 1144 of the screw driver 1140cooperate to form a screw coupling 1162 that releasably couples thescrew driver 1140 to pedicle screw 1100. In the embodiment illustratedin FIGS. 37A-38E, the screw coupling 1162 is formed by the blunt end1160 of the inner shaft 1144 and the internally threaded distal end 1164of the outer sleeve 1142. The distal end 1164 of the outer sleeve 1142forms a socket 1166 around the fixation element and the distal end 1160of the inner shaft 1144 serves as the bottom of the socket 1166. Thescrew coupling 1162 has an unlocked configuration, in which the fixationelement and the screw driver 1140 are separable. The screw coupling 1162also has a locked configuration, in which the fixation element and thedriver 1140 are inseparable. Furthermore, in the locked configuration,the screw coupling 1162 transmits torque from the driver 1140 to thefixation element in order to thread the fixation element into a pedicleor other part of a bone.

The operation of the lever 1148 to select the unlocked or lockedconfiguration is as described above with regard to screw driver 1130.However, due to the relative locations of the pivot points between thelever 1148 and handle 1146 and between the lever 1148 and a first end ofthe coupling element 1150, the motion of inner shaft 1144 is reversedcompared to screw driver 1130. When the free end of the lever 1148 islifted away from the handle 1146, the inner shaft 1144 is pulled awayfrom the distal end of the outer sleeve 1142. When the lever 1148 isrotated to lie generally flat against the handle 1146, the inner shaft1144 is pushed toward the threaded distal end 1164 of the outer sleeve1142. In a preferred embodiment, the blunt distal end 1160 of the innershaft 1144 may lie at a precisely controlled predetermined depthrelative to the threaded distal end 1164 of the outer sleeve 1142 whenscrew driver 1140 is in the locked position.

It can be appreciated that the screw driver 1140 may also be used withfixation member 302 or 352, since the screw coupling 1162 is configuredto engage the proximal threads and the proximal end of the fixationmember.

The lever and coupling element may be replaced in alternate embodimentscrew drivers with other means of selecting between the unlocked andlocked configurations. For example, the lever and coupling element maybe replaced with a mechanism that includes a knob that threads directlyor indirectly to the inner shaft to move the inner shaft with respect tothe outer sleeve. In such an embodiment, turning the knob clockwise, forexample, may move the inner shaft away from the distal end of the outersleeve, while turning the knob counterclockwise may move the inner shafttoward the distal end of the outer sleeve.

FIG. 39 illustrates an embodiment of a base reamer 1250. The base reamer1250 comprises a replaceable reamer tip 1252, an outer sleeve 1254, anoptional inner shaft 1256, and a torque fitting 1258. The base reamer1250 may cooperate with a shield (not shown), which may be a tube sizedto slide over at least the reamer tip 1252 to isolate the reamer tip1252 from surrounding soft tissues.

The replaceable reamer tip 1252 comprises a first cutting portion 1260,a second cutting portion 1262, a center bore 1274 and a shaft portion1264. The first cutting portion 1260 and second cutting portion 1262 maybe configured to correspond to a particular implant base embodiment.Therefore, a set of reamer tips may be provided, wherein each reamer tipin the set corresponds to a different implant base configuration. Thefirst cutting portion 1260 is at the distal end of the reamer tip 1252,and may comprise side cutting flutes 1266, or end cutting flutes 1268,or both. An embodiment having both side-1266 and end-cutting 1268 flutesis shown in FIG. 39. First cutting portion 1260 may cut a cylindricalhole, a conical hole, or some other shape. First cutting portion 1260may be windowed, as shown. The second cutting portion 1262 is proximallyadjacent to first cutting portion 1260, and may comprise side cuttingflutes 1270, or end cutting flutes 1272, or both. An embodiment havingboth side-1270 and end-cutting 1272 flutes is shown in FIG. 39. Secondcutting portion 1262 cuts a larger diameter hole adjacent to the holecut by first cutting portion 1260. The transition between the smallerdiameter of first cutting portion 1260 and the larger diameter of secondcutting portion 1262 may be flat as shown, i.e., perpendicular to thecenter axis 1261 of the cutting portions 1260, 1262, conical, convex,concave, or it may comprise a gradually curving transition, depending onthe configuration of the corresponding implant base. For at least someembodiments, the combined transition and larger diameter hole can beconsidered a counterbore or a spot face. A counterbore is a largerdiameter added at the open end of a smaller diameter hole, with a flatsurface between the two diameters, which may be for the purpose ofcreating a recessed space for the head of a fastener. A spot face is ashallow, larger diameter added at the top of a hole, which may be forthe purpose of creating a flat surface around the hole. Center bore 1274extends through the full length of reamer tip 1252. Bore 1274 is sizedto spin freely over the proximal threaded attachment portion and shaftof any of the fixation members or pedicle screws described herein. Shaftportion 1264 comprises a threaded interconnection 1265 to removablyconnect reamer tip 1252 to outer sleeve 1254, although otherinterconnections that permit the reamer tip 1252 to be exchanged on theouter sleeve 1254 are contemplated within the scope of this invention.

Outer sleeve 1254 is generally tubular. Outer sleeve 1254 may have oneor more proximal windows 1276 and an external target such as line 1278shown in FIG. 39.

Optional inner shaft 1256, if present, is slidably retained within outersleeve 1254. Inner shaft 1256 comprises a depth indicator portion 1286at or near the proximal end 1290 of inner shaft 1256. The depthindicator portion 1286 is marked with a line 1288. Inner shaft 1256 alsocomprises a blunt distal end 1292 that extends into the bore 1274 of thereamer tip 1252.

Torque fitting 1258 is rigidly affixed to the proximal end of the outersleeve 1254. In the embodiment shown, the torque fitting 1258 is a shaft1282 terminating in a quick connect tip 1284 suitable for connection toa modular handle or power driver (not shown). However, other torquefittings are contemplated, such as a square tip, hexagonal tip, threads,manual handle, or other fittings known in the art. In the embodimentshown, a proximal interior end surface 1280 of torque fitting 1258closes the proximal end of outer sleeve 1254, although in alternateembodiments the proximal end of outer sleeve 1254 may be closed byanother component part, or by an intrinsic portion of outer sleeve 1254.

Inner shaft 1256 slides between a distal limit and a proximal limit. Thedistal limit may occur when a protruding distal edge of depth indicatorportion 1286 contacts a distal edge of proximal window 1276 on outersleeve 1254. However, the distal limit may occur when another portion ofthe inner shaft 1256 contacts a portion of the base reamer 1250. Wheninner shaft 1256 is at its distal limit, its blunt distal end 1292 is atits closest approach to the distal end of the reamer tip 1252, and theline 1288 is distal to the target line 1278 on outer sleeve 1254. In theembodiment shown, the proximal limit occurs when the proximal end 1290of inner shaft 1256 abuts the proximal interior end surface 1280 oftorque fitting 1258. However, the proximal limit may occur when anotherportion of the inner shaft 1256 contacts a portion of the base reamer1250. When inner shaft 1256 is at its proximal limit, the blunt distalend 1292 may be at a precisely controlled predetermined depth from areference feature, such as the distal end of the reamer tip 1252, andthe line 1288 may be precisely aligned with the target line 1278 onouter sleeve 1254.

FIG. 40 illustrates an embodiment of a base broach 1350. The base broach1350 comprises a replaceable broach tip 1352, an outer sleeve 1354, anoptional inner shaft (not shown), and a hammer handle 1358. The basebroach 1350 may cooperate with the shield described previously.

The replaceable broach tip 1352 comprises a body 1360, an optionalflange 1362, a center bore 1364, and a shaft portion 1366. The body 1360and optional flange 1362 may be configured to correspond to a particularimplant base embodiment. Therefore, a set of broach tips may beprovided, wherein each broach tip in the set corresponds to a differentimplant base configuration. The body 1360 may comprise a plurality ofoptional fins 1368 if the corresponding implant base has fins or othersimilar projections. The fins 1368, if present, may be provided withcutting features, such as teeth, serrations 1370, or blades. Theoptional flange 1362 forms a shelf proximally adjacent to the body 1360and corresponding to a flanged implant 7, base. The center bore 1364comprises a diameter 1384 sized to slip over the proximal threadedattachment portion and shaft of any of the fixation members disclosedherein. The center bore 1364 may further comprise a plurality of flats1372 corresponding in number to, and sized to slip over, the flats 1107on pedicle screw 1100. In this case, the broach tip 1352 would bededicated for use only with fixation members having a correspondingplurality of flats 1107. The shaft portion 1366 comprises aninterconnection 1374 to removably connect broach tip 1352 to outersleeve 1354, and it may be similar or identical to the shaft portion1264 described above with regard to the base reamer 1250.

The outer sleeve 1354 is generally tubular. Outer sleeve 1354 may haveone or more proximal windows 1376 and an external target such as a line(not shown) similar to line 1278 of outer sleeve 1254 of base reamer1250. Outer sleeve 1354 may be functionally or physically similar oridentical to outer sleeve 1254.

The optional inner shaft, if present, is slidably retained within outersleeve 1354. The inner shaft may be functionally or physically similaror identical to inner shaft 1256 of base reamer 1250.

The hammer handle 1358 comprises a solid shaft 1378 between two sturdyflange portions 1380, 1382. The shaft 1378 and flange portions 1380,1382 may be integrally formed, permanently assembled, such as by weldingseparate pieces, or separably assembled. In the embodiment shown, hammerhandle 1358 is configured with a distal bore to rigidly affix to outersleeve 1354. Alternatively, the hammer handle 1358 may be integrallyformed with the outer sleeve 1354. At least one of the flange portions1380, 1382 may have a feature, such as flat 1386, to indicate theorientation of any fins or other projections on the broach tip 1352.

FIGS. 41-42 illustrate the base inserter 1400 alone and in combinationwith modular handle 1410.

In this embodiment, the base inserter 1400 comprises a monolithic shaftwith a distal end 1402 and a proximal end 1404. The distal end 1402 hasa bore 1406, which may comprise a precisely controlled predetermineddepth, and a threaded portion 1408, whose threads cooperate with thethreaded lumens of implant base 354 or 870. The proximal end 1404comprises a threaded portion 1412 and terminates in a flattened portion1414.

The modular handle 1410 comprises a distal collet 1416, an interior slot1418, an outer sleeve 1420, a spring 1422, and a proximal platform 1424.Handle 1410 may be characterized as a quick connect handle because itcan be attached and removed from an instrument shaft, such as baseinserter 1400, faster than, for example, threading a handle onto ashaft. The collet 1416 has a plurality of prongs 1426 which flare towardthe open end of the collet 1416 in the free state. The prongs 1426 havethreads 1428 on their inner faces which cooperate with the threads 1412on the base inserter 1400 when the collet 1416 is retracted within outersleeve 1420. The collet 1416 is rigidly assembled to slot 1418, which isshaped and sized to surround and cooperate with the flattened portion1414 on the base inserter 1400. The collet 1416 and the slot 1418 arerigidly assembled to, or integrally formed with, the platform 1424. Theouter sleeve 1420 slides over the collet 1416 such that the prongs 1426are compressed together when the collet 1416 is retracted within theouter sleeve 1420, and uncompressed when the collet 1416 extends atleast partially out of the outer sleeve 1420. The spring 1422 biases theouter sleeve 1420 toward the open end of the collet 1416 so that thecollet 1416 is normally compressed. The collet 1416 opens only when theouter sleeve 1420 slides toward the proximal platform 1424 against theresistance of spring 1422.

In an alternate embodiment (not shown), a base inserter may comprise adepth stop or depth indicator assembly that is functionally orphysically similar or identical to the outer sleeve 1254 and inner shaft1256 described previously with regard to the base reamer 1250.

In another alternate embodiment (not shown), a base inserter maycomprise a lobed distal tip corresponding to the tool engagement rims ofimplant base 304, 850, 880, 890, 900, 910, 920, or 930 instead of thethreads 1408 disclosed for base inserter 1400.

FIG. 43 illustrates an inserter 1500 for a superior facet joint implant,such as implant 210 disclosed herein. The superior inserter 1500comprises a fixed jaw 1502, a moveable jaw 1504, a bar 1506, a lever1508, and a handle 1510.

The fixed jaw 1502 comprises a shaft 1512, with a distal arm 1514terminating in a tab 1516, and an elbow 1518 at the proximal end. Theshaft 1512 may be grooved along at least one side, as shown. The tab1516 is sized and shaped to fit into a first notch 206 on superior facetjoint implant 210. Because the tab 1516 and notch 206 are noncircular,their engagement assures a particular orientation between the superiorimplant 210 and the inserter 1500. The elbow 1518 creates a visuallyobvious angle with respect to the shaft 1512, and may preferably be 90degrees.

The moveable jaw 1504 is hinged to the fixed jaw 1502 between the shaft1512 and arm 1514. The moveable jaw 1504 comprises an arm 1520terminating in a tab 1522. The moveable jaw 1504 is hinged to the fixedjaw 1502 such that the arm 1520 is aligned opposite the arm 1514 and thetab 1522 is aligned opposite the tab 1516. The tab 1522 is sized andshaped to fit into a second notch 206 on superior facet joint implant200 or 210. Because the tab 1522 and notch 206 are noncircular, theirengagement assures a particular orientation between the implant 200 or210 and the inserter 1500.

A first end of the bar 1506 is hinged to the moveable jaw 1504 at an endopposite the tab 1522. Furthermore, the hinge 1507 (not shown) betweenthe bar 1506 and the moveable jaw 1504 is offset from the hinge 1505between the moveable jaw 1504 and the fixed jaw 1502, although the twohinges may be close together. A second end of the bar 1506 is hinged tothe lever 1508.

The lever 1508 is hinged to the fixed jaw 1502 at or near the elbow1518. The lever 1508 is also hinged to the second end of the bar 1506.The hinge 1509 between the lever 1508 and the bar 1506 is offset fromthe hinge 1511 between the lever 1508 and the fixed jaw 1502, althoughthe two hinges may be close together.

The handle 1510 is secured to the fixed jaw 1502 at or near a free endof the elbow 1518, such that the handle 1510 lies in the same plane asthe shaft 1512 and elbow 1518. The handle 1510 extends along the angleestablished by the elbow 1518 with respect to the shaft 1512 so that theangle is more readily distinguished.

The lever 1508, bar 1506, moveable jaw 1504, and hinges 1505, 1507,1509, 1511 cooperate to provide a mechanism that allows the surgeon toopen the moveable jaw 1504 by lifting the lever 1508, and close themoveable jaw 1504 by depressing the lever 1508.

FIGS. 43-44 illustrate an embodiment of a lockout tool 1600. The lockouttool 1600 comprises a tube 1602, a hub 1604, a drive sleeve 1606, twolinks 1608, a first handle 1610, a second handle 1612, and six pins1614.

The tube 1602 comprises a distal end 1616 and a proximal end 1618. Thedistal end 1616 may or may not have a reduced diameter 1620 compared toa midportion 1622 of the tube 1602. The proximal end 1618 has a reduceddiameter 1624 compared to the midportion 1622 of the tube 1602.

The hub 1604 comprises a center body 1626 with a through hole 1628. Thecenter body 1626 has two ears or projections 1630 that extend fromopposite sides of the body. Each projection 1630 has a through hole 1632sized to receive a pin 1614. The through holes 1632 in the projections1630 are oriented perpendicular to the through hole 1628 in the body1626, and parallel to each other. The hub 1604 fits over the proximalreduced diameter 1624 immediately adjacent to the midportion 1622 of thetube 1602. The hub 1604 is securely fixed to the tube 1602, or the hub1604 may be integrally formed with the tube 1602.

The drive sleeve 1606 comprises a center body 1634 with a through hole1636. Two ears or projections 1638 extend from one side of the body1634. The projections 1638 are aligned with each other so as to bracketa space between them. A hole 1640 extends through both projections 1638.The hole 1640 is sized to receive a pin 1614. The hole 1640 in theprojections 1638 is oriented perpendicular to the through hole 1636 inthe body 1634. Two more identical projections 1642 extend from theopposite side of the body 1634 and have hole 1643 passing through them.The drive sleeve 1606 fits over the proximal reduced diameter 1624immediately adjacent to the hub 1604. The drive sleeve 1606 is able toslide along the reduced diameter 1624.

The link 1608 in this embodiment is a flat bar with an oval profile.Each end of the link 1608 is pierced with a hole 1644 sized to receive apin 1614. The holes 1644 are oriented perpendicular to the opposed flatfaces of the link 1608 and parallel to each other. One end of a firstlink 1608 is hinged between projections 1638 on drive sleeve 1606 by pin1614, and one end of a second link 1608 is hinged between projections1642 by a second pin 1614.

The first handle 1610 is a flat, generally elongate bar with an elbow1646 or dogleg at its distal end 1648. The elbow 1646 comprises two earsor projections 1650 that extend from the main portion of the firsthandle 1610. The projections 1650 are aligned with each other so as tobracket a space between them. Two holes 1652 extend through bothprojections 1650. The holes 1652 are sized to receive pins 1614. Theholes 1652 are oriented perpendicular to the opposed flat faces of thefirst handle 1610 and parallel to each other. A first hole 1652, whichis closer to the free end of the elbow 1646, hinges the first handle1610 to a first projection 1630 on hub 1604 by a pin 1614. A second hole1652, which is closer to the bend of the elbow 1646, hinges the firsthandle 1610 to a second end of the first link 1608. As the first handle1610 rotates about its hinge with the hub 1604, its hinge with link 1608rotates as well, causing the link 1608 to push or pull on its hinge withthe drive sleeve 1606. Thus, rotating the first handle 1610 causes thedrive sleeve 1606 to slide along the proximal reduced diameter 1624 ofthe tube 1602.

The second handle 1612 is also a flat, generally elongate bar with anelbow 1654 or dogleg at its distal end 1656. The second handle 1612further comprises a projection 1658 from its midsection 1660. The elbow1654 comprises two ears or projections 1662 that extend from the mainportion of the second handle 1612. The projections 1662 are aligned witheach other so as to bracket a space between them. Two holes 1664 extendthrough both projections 1662. The holes 1664 are sized to receive pins1614. The holes 1664 are oriented perpendicular to the opposed flatfaces of the second handle 1612 and parallel to each other. A first hole1664, which is closer to the free end of the elbow 1654, hinges thesecond handle 1612 to a second projection 1630 on hub 1604 by a pin1614. A second hole 1664, which is closer to the bend of the elbow 1654,hinges the second handle 1612 to a second end of the second link 1608.As the second handle 1612 rotates about its hinge with the hub 1604, itshinge with link 1608 rotates as well, causing the link 1608 to push orpull on its hinge with the drive sleeve 1606. Thus, rotating the secondhandle 1612 also causes the drive sleeve 1606 to slide along theproximal reduced diameter 1624 of the tube 1602.

The projection 1658 extends from the midsection 1660 of the secondhandle 1612 on the side opposite the elbow 1654. In the embodimentshown, the projection 1658 is generally arcuate. The projection 1658 ispreferably spaced about a hands′-span from the proximal end 1666 of thesecond handle 1612. The second handle 1612 may also comprise an integralplate 1668. If present, the plate 1668 is located between the opposedflat faces of the second handle 1612. The plate 1668 may extend from thedistal end 1656 to a point just past the projection 1658. The plate 1668is separated from the rest of the second handle 1612 by a slot 1670which borders three sides of the plate 1668 so that the plate connectsto the second handle 1612 only at the distal end 1656. The slot 1670 iscut parallel to the opposed flat faces of the second handle 1612. Theplate 1668 serves a passive role as an indicator of the force applied tothe first and second handles 1610, 1612 of the lockout tool 1600. As theuser grips the handles 1610, 1612 with increasing force, the handles1610, 1612 will deflect proportionately. The plate 1668 is subject to noforce and therefore experiences no deflection. As the handle 1612deflects, it appears as though plate 1668 emerges from its slot 1670 inhandle 1612, particularly at projection 1658. The deflection of handle1612 may be calibrated so that a first line 1670 marked across plate1668 and projection 1658 aligns with a second line 1672 marked acrossprojection 1658 when an appropriate grip force has been applied to thehandles 1610, 1612.

FIGS. 45-46 illustrate an embodiment of an inferior trial assembly 1700.Inferior trial 1700 comprises a trial strut 1702, a trial sphere 1704, atrial shell 1708, a trial ball 1706, and a retaining ring 1710. Inferiortrial 1700 substantially mimics inferior facet joint implant 100 (FIGS.1-6).

The trial strut 1702 substantially mimics the inferior strut 104 ofinferior facet joint implant 100. The trial strut 1702 is generallyelongated, with a central portion 1740, a first end which is a ring1742, and a second end which is a strut post 1744. The central portion1740 may be shaped to smoothly transition from the ring 1742 to thestrut post 1744, and may be straight, bent or curved. The ring 1742 maybe a generally circular feature with a center point 1746 and opposed endfaces 1748 which are substantially planar and parallel. The ring 1742may be set at an angle relative to the central portion 1740 or the strutpost 1744. The strut post 1744 may be a generally cylindrical featurewith a center axis 1750. The strut post 1744 may have a groove 1752 ator near its free end. The strut post 1744 may be at an angle relative tothe central portion 1740 and the ring 1742. A kit of trials struts maybe provided, wherein each trial strut corresponds to a matching inferiorimplant strut.

More precisely, each trial strut may be constructed so that the tip ofthe strut post is offset from the center point of the ring by one ormore of the X2 offset, the Y2 offset, and the Z2 offset describedpreviously with regard to the inferior implant strut 104

The trial sphere 1704 substantially mimics the split spheres 306 or 356shown in FIGS. 5-10. The trial sphere 1704 is sized to fit over thetapered portion of an implant base, and may have a tapered inner wall1756. The inner wall 1756 may alternatively comprise one or morediscrete diameters. The trial sphere 1704 may also have a flange 1754which encircles one open end of the trial sphere 1704. The trial sphere1704 lacks any slits, and is therefore not expandable like the splitspheres 306 or 356. The trial sphere 1704 is polyaxially mobile withinthe ring 1742 of the trial strut 1702 in the same way that split spheres306 or 356 engage the ring 182 of the inferior strut 104.

The trial shell 1708 comprises an articular body portion 1722 thatsubstantially mimics the inferior articular body 102 shown in FIGS. 1-4.Trial shell 1708 also incorporates a clip portion 1724 which is similarto clip 550 shown in FIGS. 12-14 or clip 1200 shown in FIGS. 23-25.

The articular body portion 1722 has a substantially concave interiorcavity 1712 which is defined by an interior wall 1714. A first chamferedopening 1716 and a second chamfered opening 1718 in the articular bodyportion 1722 create a passageway through which a portion of the trialstrut 1702 may fit when the inferior trial 1700 is assembled. A thirdopening 1720, which may also be chamfered, is situated orthogonal to thefirst and second chamfered openings 1716, 1718. The chamfered openings1716, 1718, 1720 may provide additional range of motion between thetrial shell 1708 and the trial strut 1702 as the trial shell 1708 ispolyaxially adjusted to fit the patient's anatomy. A trial inferiorarticular surface 1722 is located on the exterior of the articular bodyportion 1722, and is shaped like inferior articular surface 122 ofinferior facet implant 100. However, trial inferior articular surface1722 may be offset, or recessed into the articular body portion 1722,compared to inferior articular surface 122.

The clip portion 1724 comprises a body 1726, which is connected to thearticular body portion 1722 between the third opening 1720 and the trialinferior articular surface 1722, and a pair of parallel pins 1728 whichextend beside the trial inferior articular surface 1722. The body 1726may be integrally formed with the articular body portion 1722. The body1726 forms a collar 1734 surrounding a hole 1730, which may besubstantially parallel to the pins 1728. The hole 1730 may extendthrough the body 1726, and may step down to a smaller diameter 1732 atthe end closest to the pins 1728. At the same end, the collar 1734 mayflare into a platform 1736 to which the pins 1728 are connected. Thepins 1728 may be integrally formed with the platform 1736. The pins 1728may step down to a smaller diameter 1738 at their free ends.

The trial ball 1706 substantially mimics the attachment mechanism 106shown in FIGS. 1-4. More specifically, the trial ball 1706 mimics thefunctions of the conical expander 126 and split shell 128. The trialball 1706 comprises a sphere 1758 with a blunt post 1760 extending fromthe sphere 1758. The sphere 1758 has a through hole 1762 through itscenter and perpendicular to the post 1760. The sphere 1758 may also havea slit 1764 which is on the side opposite the post 1760 and whichextends the length of the hole 1762. The trial ball 1706 is polyaxiallymobile within the cavity 1712 of the trial shell 1708 in the same waythat conical expander 126 and split shell 128 engage the cavity 112 ofthe inferior articular body 102. The sphere 1758 fits inside the cavity1712, the post 1760 extends through the third opening 1720, and the hole1762 slides over the strut post 1744.

The retaining ring 1710 is circular with a gap 1766. The retaining ring1710 fits snugly in the groove 1752 on the trial strut 1702. Theretaining ring 1710 prevents the trial ball 1706 and trial shell 1708from sliding off the free end of the strut post 1744 after the inferiortrial 1700 has been assembled.

A first embodiment of an inferior inserter 1800 is shown in FIGS. 47-48.The inferior inserter 1800 comprises an inner shaft 1802, a followershaft 1804, an outer sleeve 1806, a fixed handle 1808, a movable handle1810, a lever 1812, a rod 1814, a spring 1816, a collar 1818, a smallpin 1820, three medium pins 1822, and a large pin 1824.

The inner shaft 1802 is generally cylindrical with a flared distal end1826 and a cross hole 1828 through a proximal end 1829.

The follower shaft 1804 is generally cylindrical with a distal socket1830 and cross hole 1832, and a proximal tab end 1834 with opposing flatfaces 1836. Each proximal face 1836 has a cylindrical prong 1838extending from it. Alternatively, a separate pin may be secured throughthe tab end 1834 so that the pin extends from the flat faces 1836. Thesocket 1830 is sized to receive the proximal end 1829 of the inner shaft1802. The follower shaft 1804 is fixed to the inner shaft 1802 bypassing a small pin 1820 through the cross holes 1828, 1832.

The outer sleeve 1806 is generally tubular and may be windowed. Thedistal end 1840 has a reduced diameter tip 1842 which is split into fourprongs 1844 by four slots 1846. The inside diameter of the outer sleeve1806 flares toward the distal end 1840. The proximal end 1848 of theouter sleeve 1806 may also have a reduced diameter 1850, which may bedifferent from the distal tip diameter 1842. The inside diameter of theouter sleeve 1806 may step up to a larger diameter at a locationproximal to the reduced-diameter distal tip 1842. The outer sleeve 1806slides over the inner shaft 1802. The flared inside diameter of thedistal tip 1840 of the outer sleeve 1806 fits over the flared distal end1826 of the inner shaft 1802.

The fixed handle 1808 comprises an arm 1852 with an elbow 1854 at afirst end. A second end of the arm 1852 may terminate in a loop 1856sized to fit one or more fingers or the whole hand. The arm 1852 has awindow 1858 through its midsection, in a direction generally parallel tothe free end of the elbow 1854. The arm 1852 has a cross hole 1860 whichpasses across the window 1858. The free end of the elbow 1854 comprisesa collar 1862 with a through hole 1864 sized to receive the proximal end1848 of the outer sleeve 1806. The through hole 1864 may step up to alarger diameter at its distal end. The elbow 1854 may preferablycomprise an angle near 90 degrees. Two ears or projections 1866 extendfrom the obtuse side of the elbow 1854, generally parallel to the collar1862. The projections 1866 are aligned with each other so as to bracketa space between them. Two parallel holes 1868, 1870 extend through theprojections 1866. The fixed handle 1808 is rigidly attached to the outersleeve 1806. Alternatively, the handle and the outer sleeve 1806 may bemade as a single part.

The movable handle 1810 comprises an arm 1872 with an enlarged,flattened first end 1874. A second end 1876 of the arm 1872 mayterminate in a loop 1878 sized to fit one or more fingers or the wholehand. The arm 1872 has a window 1880 through its midsection, in adirection generally parallel to a plane established by the first end1874. A terminal portion of the first end 1874 is divided into two earsor projections 1882 which are aligned with each other so as to bracket aspace between them. A through hole 1884 and an open-ended slot 1886 passthrough both projections 1882. The first end 1874 of the arm 1872 alsohas a through hole 1888 and slot 1890 located between the window 1880and the projections 1882. The first end 1874 of the movable handle 1810slides between the projections 1866 on the fixed handle 1808. Themovable handle 1810 is pivotally attached to the fixed handle 1808 bypassing the large pin 1824 through the hole 1890 and the hole 1868. Amedium pin 1822 passes through the hole 1870 and the slot 1890 to limitthe pivotal motion of the movable handle 1810. The projections 1882 onthe movable handle 1810 slide over the tab end 1834 of the followershaft 1804 and the open-ended slot 1886 receives the prongs 1838 or pinends of the follower shaft 1804. This arrangement turns pivotal movementof the movable handle 1810 into linear movement of the follower shaft1804 and inner shaft 1802 within the outer sleeve 1806.

The lever 1812 may be generally arcuate. A first end of the lever 1812is divided into three projecting tabs. The first two tabs 1892 areparallel and aligned with each other so as to bracket a space betweenthem. A hole 1894 passes through both tabs 1892 near their free ends.The third tab 1896 is perpendicular to the first two tabs 1892, andextends beside the first two tabs 1892 so that the three tabs form athree-sided, slotted channel. The midportion of the lever 1812 has awindow 1898 oriented generally parallel to the first two tabs 1892. Theedge of the window 1898 closest to the tabs may have serrations 1798,threads, or other tooth-like features. The first two tabs 1892 of thelever 1812 slide over the arm 1872 of the movable handle 1810 so thatthe lever 1812 may be pivotally attached to the movable handle 1810 bypassing a medium pin 1822 through the hole 1894 and the hole 1888. Thethird tab 1896 rests against the arm 1872 between the window 1880 andthe first end 1874. In this arrangement, the third tab 1896 may functionas an intrinsic spring that biases the lever 1812 to lie against themovable handle 1810.

The rod 1814 is generally cylindrical. The outside diameter of the rod1814 may step down one or more times from a first end 1796 to a secondend 1794. The first end 1796 comprises a tab 1792 with opposing flatfaces 1790. A through hole 1788 pierces the flat faces 1790 of the tab1792. The first end 1796 of the rod 1814 is sized and shaped to slideinto the window 1858 in the arm 1852 of the fixed handle 1808 so thatthe rod 1814 may be pivotally attached to the fixed handle 1808 bypassing a medium pin 1822 through the hole 1788 and the hole 1860. Thesecond end 1794 of the rod 1814 is sized and shaped to slide into thewindow 1880 in the arm 1872 of the movable handle 1810 and further intothe window in the midportion of the lever 1812. The rod 1814 fits intothe windows 1858, 1880, 1898 with clearance over the full range ofmotion of the movable handle 1810.

The spring 1816 is sized to slide over all but the largest outsidediameter of the rod 1814. In the free state, the spring 1816 may beapproximately the same length as the rod 1814.

The collar 1818 is generally tubular. A first end 1786 of the collar1818 may be angled to correspond to a facing surface on the arm of themovable handle 1810. The inside diameter of the collar 1818 may step upfrom the first end 1786 to a second end 1784 of the collar 1818. Theentire collar 1818 slides over the second end 1794 of the rod 1814 andthe second end 1784 of the collar 1818 slides over at least a portion ofthe spring 1816. When the inferior inserter 1800 is fully assembled, thespring 1816 and collar 1818 are positioned between the fixed handle 1808and the movable handle 1810, with the first end of the collar 1818against the arm 1872 of the movable handle 1810. The rod 1814, spring1816, and collar 1818 act together to bias the movable handle 1810 awayfrom the fixed handle 1808.

A second embodiment of an inferior inserter 1770 is shown in FIG. 49.This embodiment may differ from the first inferior inserter 1800 in thatit has a flexible inner shaft 1772 and a flexible outer sleeve 1776. Theremaining components may be identical to those disclosed for the firstinferior inserter 1800.

The flexible inner shaft 1772 is generally cylindrical with a sphericaldistal end 1774 and a cross hole 1828 through a proximal end 1829. Theouter diameter of the inner shaft 1772 may neck down to a smallerdiameter from the proximal end 1829 to the distal end 1774 in order toincrease the flexibility of the inner shaft 1772. The inner shaft 1772may be made from any known flexible material, such as titanium, nitinol,or other superelastic alloy.

The flexible outer sleeve 1776 is generally tubular and may differ fromthe outer sleeve 1806 in that at least a portion of the outer sleeve1776 has a pattern of interlocking tabs 1778 separated by slots 1780which enhance the flexibility of the outer sleeve 1776.

Inferior inserter 1770 may be particularly useful at certain spinallevels, such as the lumbosacral level, because the inferior inserter1770 may flex to avoid obstacles such as bony or soft tissue anatomy.The inferior inserter 1770 may also be useful in minimally invasivesurgical procedures due to its flexibility.

Returning to FIGS. 1 and 22, the fixation assembly 300 and superiorimplant 200 may be implanted into the left pedicle of vertebra 2 asfollows. It is understood that steps may occur in the order presented,or in a different sequence. It is further understood that right and leftfacet joint replacements may be implanted during the same procedure andoptionally linked via a crosslink. The pedicle is prepared forimplantation, which may include removal of natural facet surfaces andbone preparation, and may include a broaching step to shape the pedicleto receive the implant base 304. Broaching may ensure bone ingrowth andbetter mechanical retention of the base and therefore the full implantsystem. The fixation member 302 is driven into the pedicle to aprescribed or desired depth. A tapered base 304 is placed on thefixation member 302, and the bone engaging portion may be urged into thebone by pressing, tapping, or other means. A split sphere 306 is placedon the base 304, and the ring 204 of the superior implant 200 is placedover the split spheres 306 and locked down relative to the fixationassembly 300. Alternatively, the split sphere 306 may be captured in thering 204 of the superior implant 200, and the implant/ring assemblyplaced on the base 304 and locked down. A second fixation assembly 300and superior implant 210 may be implanted into the right pedicle ofvertebra 2 in a similar manner.

Referring to FIGS. 23-25, the fixation assembly 350 and superior implant210 may be implanted into the left pedicle of vertebra 2 as describedabove for fixation assembly 300 and superior implant 200, with thefollowing differences. To lock the orientation and position of thesuperior implant 210, a lockout tool (not shown) is actuated to effectthe taper lock. The lockout tool has an externally threaded inner shafttip which is engaged in the threaded lumen 366 of the tapered base 354.The lockout tool is actuated, using tensile force to simultaneously pullon the tapered base 354 with the inner shaft, and push on the flange 368of the split sphere 356 with an outer shaft. This force moves the splitsphere 356 farther onto the tapered portion 364. The split sphere 356expands and engages the ring 212 of the superior implant 210 until allmotion ceases and the position of the ring 212 is locked down. Thelockout tool is unthreaded and removed, and the capture nut 358 isthreaded into the threaded lumen 366, also capturing the flange 368 ofthe split sphere 356. The capture nut 358 is included to ensure thelong-term integrity of the lock. The top nut 360 is threaded onto thefixation member 352, and assists in holding the tapered base 354, splitsphere 356, superior implant 210, and capture nut 358 against the bonesurface. The top nut 360 and capture nut 358 may use the same driver. Asecond fixation assembly 350 and superior implant 210 may be implantedinto the right pedicle of vertebra 2 in a similar manner.

Referring to FIG. 1, fixation assembly 300 may be implanted into eachpedicle of vertebra 4 in the same manner described above for vertebra 2.The pedicles are prepared for implantation, which may include removal ofnatural facet surfaces and bone preparation, and may include a broachingstep to shape the pedicles to receive the implant bases 304. Broachingmay ensure bone ingrowth and better mechanical retention of the basesand therefore the full implant system. Fixation members 302 are driveninto the pedicles to a prescribed or desired depth. Tapered bases 304are placed on the fixation members 302, and the bone engaging portionsmay be urged into the bone by pressing, tapping, or other means.Alternatively, fixation assembly 350 may be implanted into each pedicleof vertebra 4 in the same manner described above for fixation assembly300.

Next, the components of inferior implant 100 are assembled but not yetlocked together. A split sphere 306 is captured in the ring 182 of thestrut 104, and the inferior implant/sphere assembly is placed on thetapered portion 320 of the base 304 in the left pedicle of cephaladvertebra 4. An offset distance between the inferior articular surface122 and the fixation assembly 300 may be adjusted by moving the inferiorarticular body 102, with attachment mechanism 106 contained within it,relative to the inferior strut 104. At this point, the inferiorarticular surface 122 may be aligned with the superior articular surface202 of superior implant 200, and may be temporarily clipped to thesuperior articular surfaces 202 to maintain the alignment. The inferiorimplant/sphere assembly is then locked down to the fixation assembly300. In a similar manner, the components of inferior implant 101 may beassembled, adjusted, and locked down to the fixation assembly 300 in theright pedicle of cephalad vertebra 4.

The inferior articular body 102 may be packaged with the superiorimplant 200, such that the articular surfaces 122, 202 are temporarilyclipped together in a desired alignment. In this instance, the inferiorarticular body 102 is inserted with the superior implant 200 when thesuperior implant 200 is placed and locked with the fixation assembly300. Then the inferior strut 104 and the remaining components of theinferior implant 100, including the conical expander 126, split shell128, and split clamp 110 are assembled with the inferior articular body102. The ring 182 of the inferior strut 104 is assembled with a splitsphere 306 and locked down with the inferior fixation assembly 300.After insertion of the crosslink rod 108 and final lockdown, asdescribed below, the temporary clip is removed.

Alternatively, the inferior implant 100 may be made available secured toa clip. The implant 100, with the attached clip, may be insertedadjacent to an already implanted and locked down superior implant, andthe inferior and superior implants temporarily clipped together. Theinferior strut is adjusted and locked down to its fixation assembly.After insertion of the crosslink rod 108 and final lockdown of theinferior implant, as described below, the clip is removed.

Referring to FIG. 5, the clip 550 or gripping tool may be used as ahandle to place the inferior implant articular body 470 with attachedstrut adjacent to an implanted superior implant 210 such that posts orpins on the clip 550 engage in openings on the superior implant 210, andthe inferior and superior articulation surfaces are aligned. Then theinferior strut is polyaxially adjusted and locked to a fixation assembly(not shown) in a manner similar to that described above. A crosslink maybe used to connect bilateral inferior implants, as described above. Asthe final step, the clip 550 is unlocked and removed, allowingarticulation between the inferior and superior implants along theirrespective articular surfaces.

The crosslink 108 may now be inserted through the collar 164 of thesplit clamp 110 of one inferior implant 100 or 101 and optionallythrough a prepared spinous process, and through the other collar 164 onthe remaining inferior implant 100 or 101. It is appreciated that as thecrosslink 108 is inserted, the split clamp 110 is rotatable about theclamp axis 111. Therefore, the crosslink 108 may be positioned to passthrough a spinous process, or may pass through soft tissue caudal to thespinous process. Alternatively, the crosslink 108 may be inserted beforethe inferior implants are locked down to the fixation assemblies. Theattachment mechanisms 106 of each inferior implant 100, 101 are actuatedto lock down the implants, fixing the positions of the articularsurfaces 122, the inferior struts 104 and the crosslink 108 relative totheir respective fixation assemblies 300. Post-operatively, thearticular surfaces will be capable of articulating against one another,allowing a level of natural spinal motion.

With reference to FIGS. 7, 28, and 29, one method of implanting inferiorfacet replacement implant 1230 and superior facet replacement implant210 is as follows. It is understood that steps may occur in the orderpresented, or in a different sequence. It is further understood thatright and left facet joint replacements may be implanted during the sameprocedure and optionally linked via a crosslink. Fixation assembly 350is implanted into a prepared pedicle, and ring 212 of superior implant210 is positioned and taper-locked onto the fixation assembly 350, asdescribed previously. A second fixation assembly 350 (not shown) isimplanted into the pedicle of the adjacent cephalad vertebra, minussphere 356, capture nut 358 and top nut 360. Clip 1200 and attachedinferior implant 1230 are removed from sterile packaging and coupled todelivery tool 1300. The delivery tool 1300 is manipulated to positionsphere 356 onto fixation assembly 350, and posts 1212, 1218 of the clip1200 into the holes 216, 218 of the superior facet implant 210. As theclip is positioned, polyaxial adjustment may occur at several junctures,allowing adjustment of the inferior articular surface 1234 relative tothe fixation assembly 350. Ring 182 of strut 104 may rotate about sphere356 relative to the fixation assembly 350, the position of inferiorarticular body 1232 may be adjusted along strut post 184 strut 104 tomatch the offset distance between the adjacent vertebrae, the conicalexpander 126 may rotate about the strut post 184, and the split shell128 may rotate within the inferior articular body 1232. When the clip1200 is properly positioned so that the posts 1212, 1218 fit into theholes 216, 218 and the articular surfaces 214, 1234 are aligned, thedelivery tool 1300 may be triggered to release the clip from the hook1304, and the delivery tool 1300 is removed. A crosslink such as 108 maybe positioned in the split clamp 110. The fixation assembly 350 istaper-locked relative to the sphere 356 and inferior strut 104, andcapture nut 358 and top nut 360 are added to secure the assembly. Nut130 is actuated on conical expander 126 to lock down the relativeorientation of inferior strut 104 and inferior articular body 1232, andlock the position of crosslink 108. Flexing tool 1320 is attached to theconnecting portion 1206 of the clip 1200, and activated to flex theconnecting portion. As the connecting portion 1206 of the clip 1200 isflexed, shoulder 1208 rotates relative to the axis of post 1212, andshoulder 1214 rotates relative to the axis of post 1218, and tabs 1210,1216 are urged apart, and out of slots 1236. Thus, clip 1200 is detachedfrom inferior implant 1230 and also can be urged away from superiorimplant 210.

Various methods for implanting the facet joint replacement system 10described above, and alternate embodiments thereof, will now bedescribed in relation to the instruments set forth above.

The pedicles of vertebrae 2 and 4 may be prepared for implantation ofthe fixation members according to the surgeon's preferred technique.Imaging apparatus, such as a fluoroscope or C-arm, may be used tovisualize the operative pedicles. Pedicle preparation may includeprobing or tapping each pedicle to prepare a socket to receive thefixation member. In a preferred embodiment, the pedicles of the caudalvertebra, in this example vertebra 2 (FIG. 1), may be prepared so thatthe fixation member will be inserted substantially parallel to thesuperior endplate of vertebra 2, or at an optimal angle relative to thesagittal plane 3, or both. Bone resection may be performed at this time,and may include decompression as well as partial or total facetectomy atthe operative spinal level. Alternatively, bone resection may beperformed later in the surgical procedure.

Referring to FIGS. 34-36, screw driver 1130 may be used to insert apedicle screw 1100 into each pedicle. The unlocked configuration ofscrew driver 1130 is selected by lifting the lever 1110 away from thehandle 1111. The proximal end of pedicle screw 1100 is inserted into thecollet 1112 so that it contacts the bottom of the center bore 1113. Inthis way, a predetermined length of the pedicle screw 1100 is enclosedwithin the distal end 1106 of the screw driver 1130. In a preferredembodiment, the predetermined length may be about 13 mm. The lockedconfiguration of screw driver 1130 is then selected by pressing thelever 1110 against the handle 1111. As the lever 1110 is depressed, thecollet 1112 retracts into the distal end 1106 of the outer sleeve 1101and the inner walls 1115 of the prongs 1103 are compressed by the outersleeve 1101 tightly against the flats 1107 of pedicle screw 1100. Thedistal end of the pedicle screw 1100 is threaded into the pedicle untilthe distal tip 1106 of the screw driver 1130 contacts the bone surfacearound the pedicle screw 1100. The distal tip 1106 of the screw driver1130 resists further advancement of the pedicle screw 1100 into thepedicle. The unlocked configuration of screw driver 1130 is againselected by lifting the lever 1110 away from the handle 1111, and thescrew driver 1130 is detached from the pedicle screw 1100. In this way,the pedicle screw 1100 is inserted into the bone so that a predeterminedlength of the proximal end of the pedicle screw 1100 is exposed.

Alternatively, referring to FIGS. 37-38, screw driver 1140 may be usedto insert a pedicle screw 1100 into each pedicle. The lockedconfiguration of screw driver 1140 is selected by depressing the lever1148 against the handle 1146. The proximal end of the pedicle screw 1100is threaded into the distal end 1164 of the outer sleeve 1142 until itabuts the distal end 1160 of the inner shaft 1144. In this way, apredetermined length of the pedicle screw 1100 is enclosed within thedistal end 1164 of the screw driver 1140. At this point, the inner shaft1144 resists further advancement of the pedicle screw 1100 into theouter sleeve 1142, causing the proximal threads of the pedicle screw1100 to bind in the threads in the distal end 1164 of the outer sleeve1142. The distal tip of the pedicle screw 1100 is then threaded into thepedicle until the distal tip 1164 of the outer sleeve 1142 contacts thebone surface around the pedicle screw 1100. The distal tip 1164 of thescrew driver 1140 resists further advancement of the pedicle screw 1100into the pedicle. The unlocked configuration of the screw driver 1140 isselected by lifting the lever 1148 away from the handle 1146. Thisseparates the distal end 1160 of the inner shaft 1144 from the proximalend of the pedicle screw 1100 so that the screw driver 1140 may beeasily unthreaded from the pedicle screw 1100. In this way, the pediclescrew 1100 is inserted into the bone so that a predetermined length ofthe proximal end of the pedicle screw 1100 is exposed.

Alternatively, screw driver 1140 may be used to insert other fixationelements into bone, such as fixation element 302 or 352.

Referring to FIGS. 51-52, the pedicles may be further prepared byreaming a bone socket that is sized and shaped to receive a particularimplant base. The bore 1274 of the base reamer 1250 is placed over theexposed proximal end of the pedicle screw 1100, or other fixationmember. When the base reamer 1250 is first placed over the pedicle screw1100, the inner shaft 1256 tends to slide toward its distal limit due togravity. Thus, the line 1288 is distally displaced from the target line1278 on the outer sleeve 1254. As the base reamer 1250 is rotated andadvanced over the pedicle screw 1100, the distal end 1292 of inner shaft1256 contacts the proximal end of the pedicle screw 1100. As the basereamer 1250 advances further over the pedicle screw 1100, the outersleeve 1254 advances over the now stationary inner shaft 1256 so thatline 1288 approaches line 1278. When the inner shaft 1256 reaches itsproximal limit, line 1288 is aligned with line 1278. Furthermore, theinner shaft 1256 physically resists further advancement of the basereamer 1250 into the bone. In this way, the penetration of the basereamer 1250 may be limited to a predetermined depth relative to theexposed proximal end of the pedicle screw 1100.

FIG. 52 shows a cross section through the left and right pedicle axes ofvertebra 2 with base reamer 1250 fully seated with respect to pediclescrew 1100 after reaming the bone socket. The distal tip 1292 of theinner shaft 1256 of the base reamer 1250 contacts the proximal end ofthe pedicle screw 1100 and the inner shaft 1256 is at its proximallimit. FIG. 53 provides a perspective view of the reamed bone socket.

As an alternative, the base reamer may lack a movable inner shaft 1256,and may instead have a reamer tip with a center bore having thepredetermined depth. This embodiment would provide a physical depth stopto prevent over-penetration of the base reamer into the bone, althoughno external indicator would be provided.

It can be appreciated that the surgeon would select a particular basereamer to correspond to the specific implant base that will be implantedin a given pedicle.

As an optional step, the pedicles may be broached in order to preciselyconfigure the bone socket to receive a particular implant base. Abroaching step may or may not be necessary, depending on factors such asimplant base configuration or bone quality. Certain embodiments of theimplant base may be designed with self-cutting fins or other features,so that broaching is unnecessary. However, broaching may ensure that anadequate bone socket is prepared in hard or dense bone, or for animplant base having a raised bone ingrowth surface treatment.

With reference to FIGS. 53-54, the bore 1364 of base broach 1350 isplaced over the exposed proximal end of the pedicle screw 1100, or otherfixation member if used. If present, corresponding flats 1372 and 1107must be aligned in order for the base broach to advance over the pediclescrew 1100. By aligning the corresponding flats 1372 and 1107, anyanti-rotation features present on the base broach will be oriented withrespect to the pedicle screw 1100, and as will be described presently,the corresponding anti-rotation features of the implant base will bealigned with the broached socket by the pedicle screw 1100.Alternatively, if flats are not present on the base broach and fixationmember, then any anti-rotation features on the broach may be alignedaccording to the surgeon's preference.

Once properly aligned, the base broach 1350 is advanced into the boneuntil it penetrates to a predetermined depth relative to the exposedproximal end of the pedicle screw 1100. Various means of controllingbase broach penetration are contemplated within the scope of the presentinvention. A flange 1362, if present, may contact a bone surface cut ata predetermined depth by the base reamer 1250. The flange 1362 resistsfurther advancement of the base broach into the bone. The bore 1364 ofthe base broach 1350 may comprise the predetermined depth. A movableinner shaft, similar or identical to inner shaft 1256 of the base reamer1250, may be provided in an alternate embodiment of the base broach.

FIG. 54 shows a cross section through the left and right pedicle axes ofvertebra 2 with base broach 1350 fully seated with respect to pediclescrew 1100 after broaching the bone socket. Due to the odd number offins 1368 on broach tip 1352, the cross section cuts one fin 1368 atfull height, while on the opposite side of the broach tip 1352, the body1360 is cut. The flange 1362 of the base broach tip 1352 is in contactwith a corresponding flat surface of the reamed bone socket, thus actingas a depth stop by limiting further advancement of the base broach 1350into the bone. FIG. 55 offers a perspective view of the broached bonesocket.

It can be appreciated that the surgeon would select a particular basebroach to correspond to the specific implant base that will be implantedin a given pedicle.

Referring to FIGS. 55-57, the base inserter 1400 is used to place theimplant base 870 over the pedicle screw 1100 and seat the implant base870 into the prepared bone socket in the pedicle. The threads 877 of theimplant base 870 are threaded onto the distal end 1402 of the baseinserter 1400 and modular handle 1410 is attached to the proximal end1404 of the base inserter 1400. The lumen 871 of the implant base 870 isplaced over the exposed proximal end of the pedicle screw 1100. Thecorresponding flats 873 and 1107 must be aligned in order for theimplant base 870 to advance over the pedicle screw 1100. By aligning thecorresponding flats 873 and 1107, the anti-rotation features present onthe implant base will be aligned with the broached socket by the pediclescrew 1100.

Once properly aligned, the implant base 870 is advanced into the boneuntil it penetrates to a predetermined depth relative to the exposedproximal end of the pedicle screw 1100. Various means of controlling theimplant base 870 penetration are contemplated. A flange 874, if present,may contact a bone surface cut at a predetermined depth by the basereamer 1250. The flange 874 resists further advancement of the basebroach into the bone. There may also be audible or tactile sensoryfeedback when the flange 874 contacts the bone surface. The bore 1406 ofthe base inserter 1400 may comprise the predetermined depth. A movableinner shaft, similar or identical to inner shaft 1256 of the base reamer1250, may be provided in an alternate embodiment of the base inserter.

FIGS. 56-57 show the fully seated implant base 870 in cross section.FIG. 56 shows a cross section through the left and right pedicle axes ofvertebra 2 with implant base 870 fully seated with respect to pediclescrew 1100. The flange 874 of the implant base 870 is in contact with acorresponding flat surface of the prepared bone socket, thus acting as adepth stop by limiting further advancement of the implant base 870 intothe bone. Furthermore, the bore 1406 of the base inserter 1400 acts as adepth stop by abutting the proximal end of the pedicle screw 1100. FIG.57 shows a cross section perpendicular to the pedicle axis and distal tothe flange 874.

When the implant base 870 is fully seated, the modular handle 1410 maybe removed. However, in a preferred embodiment of the surgicaltechnique, the base inserter 1400 remains attached to the implant base870 and is used in subsequent surgical steps.

Alternatively, implant base 354 may be threaded onto the base inserter1400. Implant base 354 may lack flats, and therefore may be suitable foruse with fixation element 352, which also lacks flats. In this case, thesurgeon would align any anti-rotation features of implant base 354 withthe previously broached socket.

In a further alternative, implant base 304, 850, or 880 may connect toan alternate embodiment of a base inserter (not shown) which has acomplementary distal tip to engage the tool engagement rim 322.

Referring to FIGS. 58-61, in a preferred embodiment, the superiorimplant 210 may be supplied with a split sphere 306 captive within thesuperior implant ring 212. The superior facet joint implant 210 withsplit sphere 306 may be grasped by the superior inserter 1500 byembracing the implant 210 with the arms 1514, 1520, positioning the tabs1516, 1522 to engage the notches 206 on opposite sides of the implant210, and depressing the lever 1508 to close the moveable jaw 1504. Thesuperior inserter 1500 grasps the implant 210 in a predeterminedorientation established by the engagement of the tabs 1516, 1522 and thenotches 206, and by the particular configuration of the arms 1514, 1520relative to the shaft 1512.

The ring 212 of the superior implant 210, with captive split sphere 306,is placed over the base inserter 1400 and advanced over the taperedportion 872 of the implant base 870 so that the split sphere 306contacts the tapered portion 872 and the superior articular surface 214faces medially. The superior implant 210 may then be placed in a desiredorientation by positioning shaft 1512 of the superior inserter 1500parallel with the superior endplate of the vertebra (FIG. 60).Fluoroscopic or other imaging equipment may be used to ensure the shaft1512 is properly aligned. The handle 1510 of the superior inserter 1500may also be positioned parallel to the sagittal plane 3 (FIG. 61), whilemaintaining the shaft 1512 in alignment with the superior endplate. Thesagittal plane 3 and superior endplate alignment may be maintainedduring the subsequent lockout step.

Referring now to FIGS. 62-64, the tube 1602 of the lockout tool 1600 ispassed over the base inserter 1400 and advanced to contact the flange368 of the split sphere 354, or a corresponding edge of split sphere306. The modular handle 1410 is reattached to the proximal end 1404 ofthe base inserter 1400 where it protrudes from the drive sleeve 1606 ofthe lockout tool 1600. The handles 1610, 1612 of the lockout tool 1600are squeezed together until the first line 1670, marked across the plate1668, aligns with the second line 1672, marked across the projection1658. As the handles 1610, 1612 are squeezed together, the lockout tool1600 stabilizes itself on the implant base 870 with the base inserter1400 and pushes on the split sphere 306 with the tube 1602 to lock thesuperior implant 210 to the implant base 870.

The modular handle 1410, lockout tool 1600, and base inserter 1400 areremoved. Optionally, a capture nut 358 may be threaded into the threads877 in the implant base 870. A top nut 360 is threaded onto the pediclescrew 1100 to hold the implant base 870 in the bone socket.

The surgeon may then remove the superior inserter 1500 by lifting thelever 1508 to open the moveable jaw 1504.

The pedicles of vertebra 4 may be reamed and optionally broached aspreviously described for vertebra 2. Implant bases may be inserted intothe bone sockets as previously described. The base inserters 1400, oralternate embodiments thereof, preferably stay connected to the implantbases to be used in subsequent surgical steps.

Referring to FIGS. 65-67, one or more inferior trials 1700 may be usedto determine the appropriate inferior facet joint implant 100 for aparticular operative site. As previously described, the inferior trial1700 substantially mimics the inferior facet joint implant 100.Furthermore, a kit of inferior trials 1700 may be provided, wherein eachinferior trial 1700 in the kit has a unique configuration thatcorresponds to a specific inferior facet joint implant 100configuration.

The inferior inserter 1800 is connected to a selected inferior trial1700 by inserting the reduced diameter tip 1842 of the inferior inserter1800 into the hole 1730 of the inferior trial 1700 and squeezing thehandles 1808, 1810 of the inferior inserter 1800 together to draw theflared distal end 1826 of the inner shaft 1802 further into the distaltip 1840 of the outer sleeve 1806 so that the prongs 1844 deflectoutwardly to bind within the hole 1730. The lever 1812 of the inferiorinserter 1800 is spring biased so that its serrations 1798 bind againstthe rod 1814 to lock the inferior inserter 1800 mechanism so that itwill stay connected to the inferior trial 1700 until the lever 1812 islifted. When the lever 1812 is lifted, the spring 1816 pushes themovable handle 1810 away from the fixed handle 1808 to quickly andeasily disconnect the inferior inserter 1800 from the inferior trial1700.

With the selected inferior trial 1700 connected to the inferior inserter1800, the trial sphere 1704 is passed over the base inserter 1400 andadvanced to contact the tapered portion 872 of the implant base 870. Thetrial shell 1708 is manipulated with the inferior inserter 1800 to slidethe pins 1728 into the openings 582 of the superior implant 210. If thepins 1728 cannot be fully inserted into the openings 582, then theselected inferior trial 1700 is unsuitable for the particular operativesite or patient anatomy. In this case, the inferior trial 1700 isdisconnected from the inferior inserter 1800 and a different inferiortrial 1700 is selected. The trialing process is repeated with differentinferior trials 1700 until a particular inferior trial 1700 is foundthat fits the operative site. Proper fit is demonstrated when the trialsphere is placed on the tapered portion 872 of the implant base 870 andthe pins 1728 can be fully inserted into the openings 582. The inferiortrial size is noted, and the same size inferior facet implant 100 isselected for permanent implantation.

The selected inferior facet implant 100 may be connected to the inferiorinserter 1800 by a clip, as described previously. In a preferredembodiment, the inferior facet implant 100 includes alternate inferiorarticular body 402 and a split sphere 306 captive in the ring 182 of theinferior strut 104. The inferior facet implant 100 may be providedalready coupled to the clip 410. Otherwise, the prongs 418 of the clip410 may be inserted into the gripping feature 404 of inferior articularbody 402. The angled holes 408 and the flared prongs 418 interact toretain the clip 410 on the inferior articular body 402. The inferiorinserter 1800 is connected to the clip 410 by inserting the reduceddiameter tip 1842 of the inferior inserter 1800 into the socket 414 ofthe clip 410 and squeezing the handles 1808, 1810 of the inferiorinserter 1800 together. The prongs 1844 deflect outwardly to bind withinthe socket 414, and as a result, the prongs 418 are urged apart so thatthe inferior inserter 1800 is securely connected to the inferior facetimplant 100 through the clip 410.

With the selected inferior facet implant 100 connected to the inferiorinserter 1800, the split sphere 306 is placed over the base inserter1400 and advanced to contact the tapered portion 872 of the implant base870. The inferior articular body 402 is manipulated with the inferiorinserter 1800 to slide the pins 416 of the clip 410 into the openings582 of the superior implant 210.

The lockout tool 1600 is used to lock the inferior strut 104 to theimplant base 870 in the same manner described previously. After removingthe modular handle 1410, lockout tool 1600, and base inserter 1400 areremoved, an optional capture nut 358 may be threaded into the threads877 in the implant base 870. A top nut 360 is threaded onto the pediclescrew 1100 to hold the implant base 870 in the bone socket.

Optionally, a crosslink 108 may be secured between bilateral left andright inferior facet implants 100. The crosslink 108 may be grasped byan inserter, such as a locking forcep 2100, and manipulated through theinterspinous space between vertebrae 2, 4 until each end of thecrosslink 108 passes through the collar 164 of the split ring clamp 110of each inferior facet implant 100.

The nut 130 of each inferior facet implant 100 is tightened so that thecrosslink 108 and the inferior articular bodies 402 are locked. Anoptional counter torque tool 2200 may be used to stabilize the constructas the nut 130 is tightened.

The present invention includes variances of the system herein described.Alternative embodiments may include different geometries andintermediate parts. Changes in the geometry, especially on the ends ofthe inferior strut, may be made to facilitate instrumentation or overallfunction. Applications of the present invention may include single- ormulti-level facet joint replacement, or other iterations in which a rodor rod-like member is fixed to a second member to attain spinal fusion.

System 10, and other facet replacement components disclosed herein, mayalso be implanted on multiple vertebral levels to provide facet jointreplacement across several levels. In a multi-level application,additional superior implants may be added to the fixation assemblies 300which secure the inferior struts 104, to extend the system in a cephaladdirection. Similarly, to extend the system caudally, additional inferiorstruts coupled to inferior implants may be added to the fixationassemblies 300 which secure the original superior implants 200. Also,fusion rods (not shown) may be secured between fixation assemblies 300on adjacent vertebrae to provide rigid fusion at a desired vertebrallevel.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. It isappreciated that various features of the above-described examples can bemixed and matched to form a variety of other alternatives. As such, thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. A surgical system comprising: an implantcomprising: a fixation member comprising a proximal portion and a distalportion; a base positioned around a proximal portion of the fixationmember, wherein the base comprises an upper portion and a lower portionseparated by a flange; a split sphere positioned around the upperportion of the base and entirely above the flange; a ring memberpositioned around the split sphere; and a locking nut; and a driver forengaging the fixation member.
 2. The surgical system of claim 1, whereinthe fixation member includes a first threaded portion and a secondthreaded portion.
 3. The surgical system of claim 2, wherein the firstthreaded portion is separated from the second threaded portion by anon-threaded shaft.
 4. The surgical system of claim 1, wherein the lowerportion comprises a bone engaging portion.
 5. The surgical system ofclaim 4, wherein the bone engaging portion is tapered.
 6. The surgicalsystem of claim 4, wherein the bone engaging portion comprises outwardlyprojecting fins.
 7. The surgical system of claim 1, wherein the baseincludes a central lumen that extends therethrough.
 8. The surgicalsystem of claim 1, wherein the flange has a diameter greater than boththe upper portion and the lower portion of the base.
 9. The surgicalsystem of claim 1, wherein the lower portion comprises a plurality ofholes.
 10. The surgical system of claim 1, wherein the split spherecomprises a plurality of slits which allow the split sphere to beexpandable.
 11. The surgical system of claim 1, wherein a strut extendsfrom the ring member.
 12. The surgical system of claim 1, wherein thelocking nut comprises a threaded bore and a flange.
 13. The surgicalsystem of claim 1, wherein the driver comprises an outer sleeve and aninner shaft.
 14. The surgical system of claim 1, wherein the drivercomprises an outer sleeve, an inner shaft, a handle, and a lever. 15.The surgical system of claim 1, wherein the driver comprises an outersleeve and an inner shaft, wherein the outer sleeve has one or more tabsnear a distal end.
 16. The surgical system of claim 15, wherein theinner shaft slides within the outer sleeve.
 17. The surgical system ofclaim 16, wherein the inner shaft is held in fixed rotational alignmentto the outer sleeve.
 18. The surgical system of claim 15, wherein theouter sleeve and the inner shaft cooperate to form a screw coupling thatreleasably couples the driver to the fixation member.
 19. The surgicalsystem of claim 1, wherein the fixation member is a pedicle screw andthe implant is an inferior facet implant.
 20. The surgical system ofclaim 1, wherein the upper portion of the base is tapered and increasesin width from an open end towards the flange.